CN111704939B

CN111704939B - Method for promoting lignin depolymerization by preoxidation-catalytic hydrogenolysis

Info

Publication number: CN111704939B
Application number: CN202010347048.5A
Authority: CN
Inventors: 肖睿; 刘超; 韩越; 雷鸣
Original assignee: Southeast University
Current assignee: Southeast University
Priority date: 2020-04-28
Filing date: 2020-04-28
Publication date: 2021-11-12
Anticipated expiration: 2040-04-28
Also published as: CN111704939A; WO2021218197A1

Abstract

The invention discloses a method for promoting lignin depolymerization by preoxidation-catalytic hydrogenolysis, which comprises the following steps: pre-oxidizing lignin by using 2, 3-dichloro-5, 6-dicyan p-benzoquinone (DDQ) in a solvent system; then decompressing and concentrating the mixed solution after pre-oxidation, dripping the mixed solution into water or ether for precipitation after the mixed solution is thick, collecting the precipitate, washing, freezing and drying to obtain pre-oxidized lignin; finally, pre-oxidized lignin and CuMgAlO are added_xThe catalyst and hydrogen donor solvent are placed in a high-pressure reactor, the reactor is sealed after being washed and pressurized by inert gas, and the catalytic hydrogenolysis of lignin is carried out at a certain temperature and for a certain time. The two-step method can greatly improve the total yield of monomers and dimers generated by lignin depolymerization, and avoids the use of high-pressure hydrogen through in-situ hydrogen supply of a solventThe method provides a reliable method for efficiently and safely converting lignin into the biofuel precursor, and has a good application prospect.

Description

Method for promoting lignin depolymerization by preoxidation-catalytic hydrogenolysis

Technical Field

The invention belongs to the field of biomass utilization, relates to a lignin depolymerization method, and particularly relates to a method for promoting lignin depolymerization by preoxidation-catalytic hydrogenolysis.

Background

The biomass produced by photosynthesis in the world is about 170 hundred million tons, the energy contained in the biomass is 10 times of the energy consumed by fuel all over the world, but the energy utilization rate of the biomass is less than 1 percent, and the development potential is huge; the lignin is one of three major components of the biomass, accounts for about 15-35% of the total amount of the biomass, has energy of 40%, is a unique renewable aromatic ring resource, and can be used for preparing high-energy-density liquid fuel; however, the lignin has a complex structure and is difficult to be depolymerized efficiently, and only less than 5% of lignin is utilized, so that the lignin resource is greatly wasted; therefore, it is urgently needed to develop an efficient conversion method to realize high-value utilization of lignin.

Common thermal chemical conversion modes of lignin comprise pyrolysis, combustion, gasification, liquefaction and the like, wherein the lignin liquefaction has the advantage of preparing high-energy-density liquid fuel by directional depolymerization; the lignin catalytic hydrogenolysis belongs to one of liquefaction, generally needs to be carried out under the conditions of external hydrogen, high temperature and high hydrogen pressure, has higher requirements on a reactor, reduces the safety and the economical efficiency of engineering by transporting the hydrogen, can effectively avoid the problems by adopting in-situ hydrogen supply of a solvent, and is a hydrogenation liquefaction depolymerization means with development prospect.

Reactive intermediates generated during lignin depolymerization are easily recondensed, so that the yield of monomers and dimers is reduced; theoretically, the condensation polymerization inhibition and depolymerization promotion can be realized by shielding the active sites easy to condense through lignin end-capping pretreatment; in lignin end-capping pretreatment, oxidation is one of the more common methods by converting C in the side chain structure of lignin_αOxidation of-OH to C_αO, reduction of readily condensable active sites C_α ⁺Inhibiting lignin condensation; at the same time, C is added_αOxidation of-OH to C_αThe carbon-oxygen (C-O) ether bond energy can be reduced by 40-50 kJ/mol by O, so that lignin depolymerization is easier to occur; according to the relevant literature, the Au/Li-Al LDH is adopted as the catalyst to pre-oxidize the kraft woodCarrying out oxidative depolymerization on the lignin, and increasing the total yield of the obtained monomer and dimer from 20% to 25%; carrying out catalytic hydrogenolysis on the whole components of the birch preoxidation, and increasing the yield of depolymerized monomers from 0.3mg to 3.2 mg; but the catalytic hydrogenolysis of the preoxidized zelkova lignin reduced the monomer yield from 19% to 11% and the dimer yield from 55% to 40%; therefore, in the actual conversion process, the lignin oxidation pretreatment can promote the subsequent depolymerization of the lignin under certain conditions, so that the yield of the depolymerization product is improved; but the yield of the subsequent depolymerization product of the pre-oxidized lignin under the partial depolymerization system is not improved, which indicates that the subsequent depolymerization of the pre-oxidized lignin is not promoted at this time; therefore, to facilitate the subsequent depolymerization of the pre-oxidized lignin, a suitable depolymerization system is also incorporated.

Disclosure of Invention

Aiming at the problems, the invention provides a method for promoting lignin depolymerization by preoxidation-catalytic hydrogenolysis, which can greatly improve the total yield of lignin depolymerization monomers and dimers.

The technical scheme of the invention is as follows: a method for promoting lignin depolymerization by preoxidation-catalytic hydrogenolysis comprises the following specific operation steps:

(1.1) pre-oxidizing lignin by using 2, 3-dichloro-5, 6-dicyan-p-benzoquinone (DDQ) in a solvent system;

(1.2) concentrating the mixed solution after pre-oxidation under reduced pressure, dripping the mixed solution into water or ether for precipitation after the mixed solution is thick, collecting the precipitate, washing, and freeze-drying to obtain pre-oxidized lignin;

(1.3) pre-oxidizing lignin and CuMgAlO_xThe catalyst and hydrogen donor solvent are placed in a high-pressure reactor, the reactor is sealed after being washed and pressurized by inert gas, and the catalytic hydrogenolysis of lignin is carried out at a certain temperature and for a certain time.

Further, the lignin in the step (1.1) is one of natural lignin, industrial lignin and laboratory-prepared lignin.

Further, the solvent system adopted in the pre-oxidation process in the step (1.1) is acetonitrile or 1, 4-dioxane.

Further, the amount of the 2, 3-dichloro-5, 6-dicyan p-benzoquinone in the step (1.1) is 5 to 60 wt%.

Further, the 2, 3-dichloro-5, 6-dicyan-p-benzoquinone in the step (1.1) needs to be mixed with O in the using process₂And (4) matching.

Further, the temperature of the pre-oxidation in the step (1.1) is 70-90 ℃, and the time is 1.5-3 h.

Further, the hydrogen donor solvent in the step (1.3) is one or more of water, methanol, ethanol, propanol and isopropanol.

Further, the CuMgAlO_xThe preparation method of the catalyst comprises the following steps:

(8.1) adding Cu²⁺、Mg²⁺、Al³⁺The mixed solution and NaOH solution are respectively dripped with Na₂CO₃Continuously stirring the solution;

(8.2) after the dropwise addition of the solution is finished, aging the mixed solution for 24 hours under a stirring state; then filtering the aging liquid, washing the filter residue with deionized water for 3-5 times, then placing the filter residue in an oven for drying overnight, and then grinding into powder;

(8.3) calcining the catalyst powder in a muffle furnace, and then adopting H₂Reducing and using 1% O₂Passivating to obtain reduced CuMgAlO_xA catalyst;

wherein, Cu is added²⁺、Mg²⁺、Al³⁺The mixed solution and NaOH solution are respectively dripped with Na₂CO₃The solution temperature is controlled at 50-70 deg.C and pH is controlled at 9-11 while stirring.

Further, the inert gas in the step (1.3) is one of nitrogen, helium, neon and argon; the number of times of gas washing is 3-5.

Further, the temperature of the catalytic hydrogenolysis in the step (1.3) is more than or equal to the supercritical temperature of the hydrogen donor solvent, and the reaction time is 0.5-8 h.

The invention has the beneficial effects that: (1) the lignin preoxidation-catalytic hydrogenolysis two-step method can realize the modification of DDQ preoxidation lignin and the subsequent CuMgAlO_xHydrogenation of catalytic supercritical hydrogen supply systemThe depolymerization is effectively combined, the total yield of monomers and dimers generated by the depolymerization of the lignin can be greatly improved, and the gain effect is obvious; (2) the lignin oxidation pretreatment process has simple process and easy operation, and can effectively improve the properties of lignin; (3) the method adopts the solvent for in-situ hydrogen supply, avoids the use of high-pressure hydrogen, and provides a reliable method for the safe catalytic hydrogenolysis of lignin; (4) the product obtained by the method mainly comprises alcohols, esters, saturated hexahydric alcohols and aromatic monomers, and the lignin resource is converted into a chemical product with a high added value, so that waste is turned into wealth, and the sustainable development requirement is met.

Detailed Description

In order to more clearly illustrate the technical solution of the present invention, the present invention will be further described below; obviously, the following description is only a part of the embodiments, and it is obvious for a person skilled in the art to apply the technical solutions of the present invention to other similar situations without creative efforts; in order to more clearly illustrate the technical solution of the present invention, the following further detailed description is made on the technical solution of the present invention:

a method for promoting lignin depolymerization by preoxidation-catalytic hydrogenolysis comprises the following specific operation steps:

wherein the mixed solution comprises a solution generated by pre-oxidizing lignin by DDQ and all solutions in a solvent system;

Example 1:

adding 1g of industrial lignin, 0.05g of 2, 3-dichloro-5, 6-dicyan-p-benzoquinone (DDQ) and 40ml of acetonitrile into a reaction kettle, sealing the reaction kettle, and adding high-purity O₂Purging for 3-5 times, and charging 1MPaO into the reaction kettle₂Reacting for 2 hours at 90 ℃, placing the reaction kettle in ice water for cooling after the reaction is finished, then discharging gas and opening the kettle; concentrating the pre-oxidized mixed solution under reduced pressure, dripping into water or diethyl ether for precipitation, collecting the precipitate, and freeze drying to obtain pre-oxidized lignin; 0.1g of pre-oxidized lignin and 0.1g of CuMgAlO_xThe catalyst and 2.4g ethanol are put into a reactor and reacted for 2 hours at 300 ℃, and the total yield of the monomer and the dimer after the liquid phase product obtained by the reaction is quantitatively calculated to be 36.56C% (the total yield of the unoxidized lignin depolymerization under the condition of the same depolymerization is 27.43C%).

Example 2:

adding 1g of industrial lignin, 0.15g of 2, 3-dichloro-5, 6-dicyan-p-benzoquinone (DDQ) and 40ml of acetonitrile into a reaction kettle, sealing the reaction kettle, and adding high-purity O₂Purging for 3-5 times, and charging 1MPaO into the reaction kettle₂Reacting for 2 hours at 90 ℃, placing the reaction kettle in ice water for cooling after the reaction is finished, then discharging gas and opening the kettle; concentrating the pre-oxidized mixed solution under reduced pressure, dripping into water or diethyl ether for precipitation, collecting the precipitate, and freeze drying to obtain pre-oxidized lignin; 0.1g of pre-oxidized lignin and 0.1g of CuMgAlO_xThe catalyst and 2.4g ethanol are put into a reactor and reacted for 2 hours at 300 ℃, and the total yield of the monomer and the dimer after the liquid phase product obtained by the reaction is quantitatively calculated to be 60.27C% (the total yield of the unoxidized lignin depolymerization under the condition of the same depolymerization is 27.43C%).

Example 3:

adding 1g of industrial lignin, 0.3g of 2, 3-dichloro-5, 6-dicyan-p-benzoquinone (DDQ) and 40ml of acetonitrile into a reaction kettle, sealing the reaction kettle, and adding high-purity O₂Purging for 3-5 times, and charging 1MPaO into the reaction kettle₂Reacting for 2 hours at 90 ℃, placing the reaction kettle in ice water for cooling after the reaction is finished, then discharging gas and opening the kettle; concentrating the pre-oxidized mixed solution under reduced pressure, and dripping into waterPrecipitating in water or ether, collecting precipitate, and freeze drying to obtain pre-oxidized lignin; 0.1g of pre-oxidized lignin and 0.1g of CuMgAlO_xThe catalyst and 2.4g ethanol are put into a reactor and reacted for 2 hours at 300 ℃, and the total yield of the monomer and the dimer after the liquid phase product obtained by the reaction is quantitatively calculated to be 51.39C% (the total yield of the unoxidized lignin depolymerization under the condition of the same depolymerization is 27.43C%).

Example 4:

adding 1g of industrial lignin, 0.6g of 2, 3-dichloro-5, 6-dicyan-p-benzoquinone (DDQ) and 40ml of acetonitrile into a reaction kettle, sealing the reaction kettle, and adding high-purity O₂Purging for 3-5 times, and charging 1MPaO into the reaction kettle₂Reacting for 2 hours at 90 ℃, placing the reaction kettle in ice water for cooling after the reaction is finished, then discharging gas and opening the kettle; concentrating the pre-oxidized mixed solution under reduced pressure, dripping into water or diethyl ether for precipitation, collecting the precipitate, and freeze drying to obtain pre-oxidized lignin; 0.1g of pre-oxidized lignin and 0.1g of CuMgAlO_xThe catalyst and 2.4g ethanol are put into a reactor and reacted for 2 hours at 300 ℃, and the total yield of the monomer and the dimer after the liquid phase product obtained by the reaction is quantitatively calculated to be 40.6C% (the total yield of the unoxidized lignin depolymerization under the condition of the same depolymerization is 27.43C%).

The detailed results of examples 1-4 can be seen in Table 1.

Table 1: and (3) comparing the yields of the depolymerization products of different pre-oxidized industrial lignin at the depolymerization time of 2 h:

sample (I)	Control sample	Example 1	Example 2	Example 3	Example 4
						Amount of DDQ used	0％	5％	15％	30％	60％
Monomer (C%)	21.94	32.55	56.31	47.29	36.53
						Dimer (C%)	5.50	4.01	3.96	4.10	4.08
Total yield (C%)	27.43	36.56	60.27	51.39	40.60

The data in the table show that after depolymerization in supercritical ethanol for 2h, different degrees of pre-oxidation can promote depolymerization of industrial lignin; through pre-oxidation, the yield of lignin depolymerized monomer is greatly increased, the yield of dimer is basically similar, and the total yield is also greatly increased.

Example 5:

adding 1g of wood grinding lignin, 0.15g of 2, 3-dichloro-5, 6-dicyan p-benzoquinone (DDQ) and 40ml of 1, 4-dioxane into a reaction kettle, sealing the reaction kettle, and adding high-purity O₂Purging for 3-5 times, and charging 1MPaO into the reaction kettle₂Reacting for 3 hours at 70 ℃, placing the reaction kettle in ice water for cooling after the reaction is finished, then discharging gas and opening the kettle; concentrating the pre-oxidized mixed solution under reduced pressure, dripping into water or diethyl ether for precipitation, collecting the precipitate, and freeze drying to obtain pre-oxidized lignin; 0.1g of pre-oxidized lignin and 0.1g of CuMgAlO_xThe catalyst and 2.4g ethanol are put into a reactor and reacted for 2 hours at 300 ℃, and the total yield of the monomer and the dimer after the liquid phase product obtained by the reaction is quantitatively calculated to be 92.11C% (the total yield of the unoxidized lignin depolymerization under the condition of the same depolymerization is 54.62C%).

Example 6:

adding 1g of wood grinding lignin, 0.15g of 2, 3-dichloro-5, 6-dicyan p-benzoquinone (DDQ) and 40ml of 1, 4-dioxane into a reaction kettle, sealing the reaction kettle, and adding high-purity O₂Purging for 3-5 times, and charging 1MPaO into the reaction kettle₂Reacting for 1.5h at 80 ℃, placing the reaction kettle in ice water for cooling after the reaction is finished, then discharging gas and opening the kettle; concentrating the pre-oxidized mixed solution under reduced pressure, dripping into water or diethyl ether for precipitation, collecting the precipitate, and freeze drying to obtain pre-oxidized lignin; 0.1g of pre-oxidized lignin, 0.1g of CuMgAlO_xThe catalyst and 2.4g ethanol are put into a reactor and reacted for 4 hours at 300 ℃, and the total yield of the monomer and the dimer after the liquid-phase product obtained by the reaction is quantitatively calculated to be 114.06C% (the total yield of the unoxidized lignin depolymerization under the condition of the same depolymerization is 49.32C%).

Examples 5-6 show that the preoxidation-catalytic hydrogenolysis to increase the yield of lignin depolymerization products is still suitable for natural lignin, the solvent used for the preoxidation is acetonitrile or 1, 4-dioxane, the preoxidation temperature is 70-90 ℃, and the preoxidation time is 1.5-3 h.

Example 7:

preoxidation of commercial lignin as in example 2; will be 01g of pre-oxidized lignin, 0.1g of CuMgAlO_xThe catalyst and 2.4g ethanol are put into a reactor and reacted for 0.5h at 300 ℃, and the total yield of the monomer and the dimer after the liquid-phase product obtained by the reaction is calculated quantitatively is 11.14C% (the total yield of the unoxidized lignin depolymerization under the same depolymerization condition is 9.03C%).

Example 8:

preoxidation of commercial lignin as in example 2; 0.1g of pre-oxidized lignin, 0.1g of CuMgAlO_xThe catalyst and 2.4g ethanol are put into a reactor and reacted for 1h at 300 ℃, and the total yield of the monomer and the dimer after the liquid phase product obtained by the reaction is calculated quantitatively is 29.61C% (the total yield of the unoxidized lignin depolymerization under the same depolymerization condition is 15.3C%).

Example 9:

preoxidation of commercial lignin as in example 2; 0.1g of pre-oxidized lignin, 0.1g of CuMgAlO_xThe catalyst and 2.4g ethanol are put into a reactor and reacted for 4 hours at 300 ℃, and the total yield of the monomer and the dimer after the liquid-phase product obtained by the reaction is quantitatively calculated to be 86.07C% (the total yield of the unoxidized lignin depolymerization under the condition of the same depolymerization is 36.29C%).

Example 10:

preoxidation of commercial lignin as in example 2; 0.1g of pre-oxidized lignin, 0.1g of CuMgAlO_xThe catalyst and 2.4g ethanol are put into a reactor and reacted for 8 hours at 300 ℃, and the total yield of the monomer and the dimer after the liquid phase product obtained by the reaction is calculated quantitatively is 95.35C% (the total yield of the unoxidized lignin depolymerization under the same depolymerization condition is 40.23C%).

The detailed results of examples 2 and 7-10 are shown in Table 2.

Table 2: comparison of unoxidized and pre-oxidized industrial lignin depolymerization product yields at different depolymerization times:

the data in the table compare the product yields of different depolymerization times of industrial lignin and pre-oxidized industrial lignin in supercritical ethanol; under any reaction time of 0.5-8h, the depolymerization yield of the pre-oxidized lignin is higher than that of a control experiment under the same condition.

Example 11:

preoxidation of commercial lignin as in example 2; 0.1g of pre-oxidized lignin, 0.1g of CuMgAlO_xThe catalyst and 2.4g of methanol are put into a reactor and reacted for 2 hours at 290 ℃, and the total yield of the monomer and the dimer after the liquid-phase product obtained by the reaction is quantitatively calculated to be 59.31C% (the total yield of the unoxidized lignin depolymerization under the same depolymerization condition is 25.56C%).

Example 12:

preoxidation of commercial lignin as in example 2; 0.5g of pre-oxidized lignin, 0.5g of CuMgAlO_xThe catalyst and 5g of water are put into a reactor and reacted for 2 hours at 420 ℃, and the total yield of the monomer and the dimer after the liquid-phase product obtained by the reaction is quantitatively calculated to be 20.08C% (the total yield of the unoxidized lignin depolymerization under the same depolymerization condition is 12.32C%).

Example 13:

preoxidation of commercial lignin as in example 2; 0.2g of pre-oxidized lignin, 0.3g of CuMgAlO_xThe catalyst and 3.5g of isopropanol are put into a reactor and reacted for 2 hours at 310 ℃, and the total yield of the monomer and the dimer after the liquid-phase product obtained by the reaction is quantitatively calculated to be 58.77C% (the total yield of the unoxidized lignin depolymerization under the condition of the same depolymerization is 25.94C%).

Example 14:

preoxidation of commercial lignin as in example 2; 0.05g of pre-oxidized lignin, 0.05g of CuMgAlO_xThe catalyst and 1.5g of propanol are put into a reactor and reacted for 2 hours at 320 ℃, and the total yield of the monomer and the dimer after the liquid-phase product obtained by the reaction is quantitatively calculated to be 39.74C% (the total yield of the unoxidized lignin depolymerization under the same depolymerization condition is 20.32C%).

Example 15:

preoxidation of commercial lignin as in example 2; 0.15g of pre-oxidized lignin, 0.2g of CuMgAlO_xAdding a catalyst and 3g of ethanol/water (1:1, v: v) mixed solvent into a reactor, reacting for 2h at 320 ℃, and quantitatively calculating the total yield of the monomer and the dimer after the liquid-phase product obtained by the reaction is 61.33C% (homolysis)Total yield of depolymerization of unoxidized lignin under polymerization conditions was 29.32C%).

Examples 11-15 show that hydrogen donating solvents such as one or more of water, methanol, ethanol, propanol, isopropanol can promote depolymerization of the pre-oxidized lignin.

Finally, it should be understood that the embodiments described herein are merely illustrative of the principles of embodiments of the present invention; other variations are possible within the scope of the invention; thus, by way of example, and not limitation, alternative configurations of embodiments of the invention may be considered consistent with the teachings of the present invention; accordingly, the embodiments of the invention are not limited to the embodiments explicitly described and depicted.

Claims

1. A method for promoting lignin depolymerization by preoxidation-catalytic hydrogenolysis is characterized by comprising the following steps: the specific operation steps are as follows:

(1.1) pre-oxidizing lignin by using 2, 3-dichloro-5, 6-dicyan p-benzoquinone in a solvent system;

(1.3) pre-oxidizing lignin and CuMgAlO_xPutting the catalyst and a hydrogen donor solvent into a high-pressure reactor, washing with inert gas, pressurizing, sealing the reactor, and carrying out catalytic hydrogenolysis on lignin at a certain temperature and for a certain time;

specifically, in the step (1.1), the lignin is one of natural lignin, industrial lignin and laboratory-prepared lignin;

the solvent system adopted in the pre-oxidation process is acetonitrile or 1, 4-dioxane;

the dosage of the 2, 3-dichloro-5, 6-dicyan p-benzoquinone is 5-60 wt%;

the 2, 3-dichloro-5, 6-dicyan p-benzoquinone needs to be mixed with O in the using process₂Matching;

the pre-oxidation temperature is 70-90 ℃, and the time is 1.5-3 h;

in the step (1.3), the hydrogen donor solvent is one or more of water, methanol, ethanol, propanol and isopropanol; the inert gas is one of nitrogen, helium, neon and argon; the number of times of gas washing is 3-5; the temperature of the catalytic hydrogenolysis is more than or equal to the supercritical temperature of the hydrogen donor solvent, and the reaction time is 0.5-8 h;

wherein, the CuMgAlO_xThe preparation method of the catalyst comprises the following steps: