A metal-modified functional lignin, its preparation method and application

Abstract

This invention relates to the field of chemical synthesis technology, providing a metal-modified lignin-based functional carbon, its preparation method, and its application. The preparation method includes: treating lignin using a chemical oxidation method to obtain lignin-based functional carbon; mechanically ball-milling the lignin-based functional carbon and metal acetate, washing the resulting material with ultrapure water, and vacuum drying to obtain the metal-modified lignin-based functional carbon material, which is then used to catalyze the isomerization of glucose to fructose. This invention uses lignin as a raw material to achieve the resource-based reuse of biomass; the method for obtaining the metal-modified highly active lignin-based functional carbon material is convenient, green, and safe; the metal-modified highly active lignin-based functional carbon material can not only efficiently convert glucose isomerization to fructose, but also has a short reaction time and high selectivity; the metal aluminum-modified lignin-based functional carbon catalyst obtained by this invention achieves a glucose conversion rate of 80%-100% and a fructose yield of 55%-60%.

Description

Technical Field

[0001] This invention belongs to the field of chemical synthesis technology, and particularly relates to a metal-modified functional lignin, its preparation method, and its application. Background Technology

[0002] With the fossil fuel crisis and environmental problems becoming increasingly serious, biomass, as a renewable resource, is considered the best raw material for producing high-value-added biochemicals such as 5-hydroxymethylfurfural and levulinic acid, replacing fossil resources. The isomerization of glucose to fructose is a key step in biomass refining. Compared to traditional methods such as bioenzyme-based fructose preparation, which suffer from harsh conditions, high costs, and easy deactivation, heterogeneous metal catalytic systems have attracted increasing attention.

[0003] However, current solid catalysts suffer from cumbersome synthesis processes, demanding conditions, low activity, and poor selectivity, necessitating further optimization to ultimately obtain fructose. To address this, we propose a metal-modified functional lignin, its preparation method, and its applications. This invention uses lignin as a carbon source and synthesizes a metal-modified functional lignin catalyst in two steps via chemical oxidation and mechanical ball milling. In an ethanol reaction system, this catalyst selectively catalyzes the isomerization of glucose to fructose, providing a promising theoretical basis for the chemical catalytic conversion of glucose to fructose. Summary of the Invention

[0004] The purpose of this invention is to provide a metal-modified functional lignin, its preparation method, and its application, in order to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for preparing metal-modified functional lignin includes the following steps:

[0007] Step S1: Treat lignin using a chemical oxidation method to obtain functional lignin;

[0008] Step S2: Mechanically ball-mill the functional lignin and metal acetate obtained in step S1;

[0009] Step S3: Wash the material obtained in step S2 with ultrapure water and vacuum dry it to obtain metal-modified functional lignin material.

[0010] Furthermore, in step S1, the oxidant used in the chemical oxidation method is one or more of hydrogen peroxide, concentrated sulfuric acid, and nitric acid; the lignin is alkali lignin, sodium lignin sulfonate, or lignin extracted from biomass.

[0011] Furthermore, in step S1, the mass ratio of lignin to oxidant used is 1:1 to 1:5.

[0012] Furthermore, in step S2, the metal acetate is aluminum acetate, iron acetate, magnesium acetate, or tin acetate.

[0013] Furthermore, in step S2, the molar mass ratio of functional lignin powder to metal acetate is 1:0.5-1:2.

[0014] A metal-modified functional lignin material prepared according to a method.

[0015] Application of a metal-modified functional lignin material in the isomerization of glucose to produce fructose.

[0016] Furthermore, the application specifically includes:

[0017] Glucose was added to ethanol to prepare a reaction solution with a substrate concentration of 5-100 g / L. The metal-modified functional lignin material was used as a catalyst. The reaction was carried out in a microwave reactor. After the reaction was completed, the supernatant was taken out and diluted. The reaction was then analyzed qualitatively and quantitatively by ultra-high performance liquid chromatography. The metal-modified functional lignin catalyst catalyzes the isomerization of glucose into fructose and its derivatives 5-hydroxymethylfurfural and 5-ethoxymethylfurfural.

[0018] Furthermore, the mass ratio of the catalyst to glucose is 1:1.5-1:10; the heating temperature is 40-160℃, and the heating time is 0.1-8 h.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] This invention utilizes lignin as a raw material to achieve the resource-based reuse of biomass. Highly active functional lignin materials are prepared through chemical oxidation, and metal-modified highly active functional lignin materials are prepared by mechanical ball milling. The synthesis route is more convenient, green, and safe. Lignin can increase its surface functionality under the action of an oxidant. Simultaneously, this invention introduces metal into the catalyst through mechanical ball milling. This material not only efficiently converts glucose isomerization to fructose, but also exhibits short reaction time and high selectivity. The results of the examples show that the aluminum-modified lignin-based functional carbon catalyst prepared by this invention achieves a glucose conversion rate of 80%-100% and a fructose yield of 55%-60%. Attached Figure Description

[0021] Figure 1 This is a TEM image of the product of the present invention.

[0022] Figure 2 This is an XPS diagram of the product of this invention.

[0023] Figure 3The yield and conversion rate of the material prepared in this embodiment of the invention for producing fructose from glucose at 140 °C for 0.5 h are shown.

[0024] Figure 4 The graph shows the change in the yield of glucose isomerization to fructose catalyzed by the material prepared in Example 3 of the present invention as a function of reaction time at different reaction temperatures. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0026] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0027] An embodiment of the present invention provides a method for preparing metal-modified functional lignin, comprising the following steps:

[0028] Step S1: Treat lignin using a chemical oxidation method to obtain functional lignin;

[0029] Step S2: Mechanically ball-mill the functional lignin and metal acetate obtained in step S1;

[0030] Step S3: Wash the material obtained in step S2, and vacuum dry it to obtain metal-modified functional lignin material.

[0031] In a preferred embodiment of the invention, the metal-modified functional lignin catalyst comprises aluminum and oxygen-containing functional groups; the aluminum exists in the form of Al. 3+ The oxygen-containing functional groups include hydroxyl and carboxyl functional groups. The oxygen-containing functional groups in the metal-modified functional lignin catalyst provided by this invention facilitate glucose adsorption and promote substrate mass transfer. Aluminum promotes the isomerization of glucose to fructose, thereby achieving highly efficient catalytic reactions.

[0032] In a preferred embodiment of the present invention, the oxidant used in the chemical oxidation method is one or more of hydrogen peroxide, concentrated sulfuric acid, nitric acid, etc.; the lignin is alkali lignin, sodium lignin sulfonate, lignin extracted from biomass, etc.

[0033] In a preferred embodiment of the present invention, in step S1, the mass ratio of lignin to oxidant is 1:(1-5), and most preferably 1:2.5.

[0034] In a preferred embodiment of the present invention, in step S1, the mixing method employs magnetic stirring, followed by static oxidation at room temperature. The rotation speed is 500-1000 rpm, preferably 600-900 rpm, and most preferably 700 rpm; the rotation time is 0.1-1 h, preferably 0.1-0.5 h, and most preferably 0.2 h; the static oxidation time is 12-24 h, preferably 16-20 h, and most preferably 18 h. The preferred oxidation method is mixing and stirring followed by static oxidation.

[0035] In a preferred embodiment of the present invention, in step S2, the metal acetate is aluminum acetate, iron acetate, magnesium acetate or tin acetate.

[0036] In this embodiment of the invention, preferably, the aluminum acetate content is 0.1-4 mol, more preferably 0.1-3 mol.

[0037] In a preferred embodiment of the present invention, in step S2, the molar mass ratio of functional lignin powder to metal acetate is 1:(0.5-2), and most preferably 1:1.

[0038] In a preferred embodiment of the present invention, in step S2, the ball milling speed is 250-400 rpm, preferably 300-400 rpm, and most preferably 350 rpm; the reaction time is 2-8 h, preferably 3-6 h, and most preferably 4 h.

[0039] In a preferred embodiment of the present invention, in step S3, the detergent used for washing is preferably water; the water is preferably ultrapure water; the amount of ultrapure water used is 10-50 mL, preferably 20-30 mL; and the number of washing cycles is preferably 1-2. The separation method during the washing process is centrifugation, with a preferred rotation speed of 10000 rpm and a preferred centrifugation time of 3 min.

[0040] The washing process is preferably as follows: the product obtained after ball milling is mixed with water and then stirred and centrifuged sequentially. The stirring time is preferably 5-10 min, the stirring rate is preferably 200-300 rpm, and the stirring method is preferably magnetic stirring.

[0041] In a preferred embodiment of the present invention, in step S3, the drying temperature is 55-80 ℃, preferably 80 ℃; and the drying time is 10-24 h, preferably 12 h.

[0042] In this embodiment of the invention, a blower drying oven, which is common in the art, is used for drying.

[0043] A metal-modified functional lignin material prepared according to a method.

[0044] Application of a metal-modified functional lignin material in the isomerization of glucose to produce fructose.

[0045] As a preferred embodiment of the present invention, the application is specifically as follows:

[0046] Glucose was added to ethanol to prepare a reaction solution with a substrate concentration of 5-100 g / L. The metal-modified functional lignin material was used as a catalyst. The reaction was carried out in a microwave reactor. After the reaction was completed, the supernatant was taken out and diluted. The reaction was then analyzed qualitatively and quantitatively by ultra-high performance liquid chromatography (UPLC). The metal-modified functional lignin catalyst catalyzed the isomerization of glucose into fructose and its derivatives 5-hydroxymethylfurfural and 5-ethoxymethylfurfural.

[0047] In this embodiment of the invention, preferably, the mass concentration of the mixture obtained after mixing the metal-modified functional lignin material as a catalyst with glucose and ethanol is 10-90 g / L. The ethanol is preferably 95% ethanol (AR), which acts only as a solvent and does not have a catalytic effect.

[0048] In a preferred embodiment of the present invention, the mass ratio of the catalyst to glucose is 1:1.5-1:10; preferably 1:2; the heating temperature is 40-160 ℃, preferably 120-160 ℃; the heating time is 0.1-8 h, preferably 0.3-2 h.

[0049] In a preferred embodiment of the present invention, the glucose isomerization reaction is preferably carried out under stirring conditions; the stirring rate is preferably 500-800 rpm; the stirring method is preferably magnetic stirring; and the equipment used for the glucose isomerization reaction is preferably a microwave reactor.

[0050] Example 1: A method for preparing metal-modified functional lignin according to an embodiment of the present invention includes the following steps:

[0051] 5 g of alkali lignin and 12.5 mL of hydrogen peroxide were placed in a 250 mL beaker and mixed by magnetic stirring. The magnetic stirring conditions were: 700 rpm for 0.2 h. After oxidation at room temperature for 18 h, the mixture was dried at 80 ℃ to obtain lignin-based functional carbon.

[0052] See Figure 1 (a) is the SEM image of the product, proving that the structure of lignin changes after oxidation.

[0053] See Figure 2 (a) is the XPS image of the product, proving that there is no metal on the surface of the material.

[0054] See Figure 3 , Figure 3 The results show the yield and conversion rate of the material prepared in Example 1 to produce fructose acid by catalytic oxidation of glucose at 140°C for 0.5 h.

[0055] Example 2: A method for preparing metal-modified functional lignin according to an embodiment of the present invention includes the following steps:

[0056] 1 g of alkali lignin was mixed with 2.04 g (2 mol) of aluminum acetate and then mechanically ball-milled (material to steel ball mass ratio 1:8). The ball milling conditions were: 350 rpm for 4 h. The mixture was then washed 1-2 times with ultrapure water, centrifuged, and dried at 80 ℃ for 12 h to obtain the metal-modified lignin catalyst material, namely Al-LS.

[0057] See Figure 1 (b) is a SEM image of the product, demonstrating that metallic aluminum is uniformly loaded onto the lignin.

[0058] See Figure 2 (b) is the XPS image of the product, proving that there is metallic aluminum on the surface of the material.

[0059] See Figure 3 , Figure 3 The results show the yield and conversion rate of the material prepared in Example 2 to produce fructose acid by catalytic oxidation of glucose at 140 °C for 0.5 h.

[0060] Example 3: A method for preparing metal-modified functional lignin according to an embodiment of the present invention includes the following steps:

[0061] (1) 5 g of alkali lignin and 12.5 mL of hydrogen peroxide were placed in a 250 mL beaker and mixed by magnetic stirring. The magnetic stirring conditions were: 700 rpm for 0.2 h. The mixture was then allowed to stand at room temperature for 18 h and dried at 80 ℃ to obtain lignin-based functional carbon.

[0062] (2) Mix 1 g of lignin-based functional carbon with 2.04 g (2 mol) of aluminum acetate and then mechanically ball mill (material to steel ball mass ratio 1:8). The ball milling conditions are: 350 rpm and 4 h. The mixture is taken out and washed with ultrapure water 1-2 times, centrifuged, and dried at 80 ℃ for 12 h to obtain metal-modified lignin catalyst material.

[0063] XPS calculations show that the aluminum acetate content in the metal-modified highly active functional lignin catalyst prepared in this embodiment is 0.1-4 mol, preferably 0.1-3 mol.

[0064] See Figure 1 (c) is a TEM image of the product, demonstrating that the metal was successfully loaded onto the lignin-based functional carbon.

[0065] See Figure 2 (c) is the XPS image of the product, proving that there is metallic aluminum on the material surface.

[0066] See Figure 3 , Figure 3 The results show the yield and conversion rate of the material prepared in Example 3 to produce fructose acid by catalytic oxidation of glucose at 140 °C for 0.5 h.

[0067] Figure 4 The graph shows the change in the yield of glucose isomerization to fructose catalyzed by the material prepared in Example 3 at different reaction temperatures as a function of reaction time.

[0068] Example 4: A method for synthesizing fructose, comprising the following steps:

[0069] 0.09 g of the lignin-based functional carbon material prepared in Example 1, 0.18 g of glucose, and 5 ml of ethanol were mixed evenly to obtain a mixture (the mass concentration of glucose in the mixture was 36 g / L, and the mass ratio of lignin-based biochar catalyst to glucose was 1:2). The mixture was then transferred to a 10 mL microwave reaction flask and placed in a microwave reactor for glucose isomerization reaction, accompanied by magnetic stirring at a stirring rate of 600 rpm. The reaction ended after 0.5 h. Subsequently, the mixture was filtered through a filter membrane, and the filtered solution was subjected to liquid chromatography to determine the product and calculate the fructose yield.

[0070] The liquid chromatography conditions were as follows: a Shodex SH1011 column, a mobile phase of 0.5 ml / min sulfuric acid solution (5 mM), a column temperature of 50 ℃, and an injection volume of 10 uL. A differential detector was used for glucose and fructose, with a detector temperature of 35 ℃.

[0071] The final fructose yield was 25.2%, and the glucose conversion rate was 51.5%.

[0072] Example 5: A method for synthesizing fructose, comprising the following steps:

[0073] 0.09 g of the metal-modified lignin catalyst material prepared in Example 2, 0.18 g of glucose, and 5 ml of ethanol were mixed evenly to obtain a mixture (the mass concentration of glucose in the mixture was 36 g / L, and the mass ratio of metal-modified lignin catalyst to glucose was 1:2). The mixture was then transferred to a 10 mL microwave reaction bottle and placed in a microwave reactor for glucose isomerization reaction, accompanied by magnetic stirring at a stirring rate of 600 rpm. The reaction ended after 0.5 h. Subsequently, the mixture was filtered through a filter membrane, and the filtered solution was subjected to liquid chromatography to determine the product and calculate the fructose yield.

[0074] The liquid chromatography conditions were as follows: a Shodex SH1011 column, a mobile phase of 0.5 ml / min sulfuric acid solution (5 mM), a column temperature of 50 ℃, and an injection volume of 10 uL. A differential detector was used for glucose and fructose, with a detector temperature of 35 ℃.

[0075] The final fructose yield was 37.1%, and the glucose conversion rate was 67.1%.

[0076] Example 6: A method for synthesizing fructose, comprising the following steps:

[0077] 0.09 g of the metal-modified highly active functional lignin catalyst prepared in Example 3, 0.18 g of glucose, and 5 ml of ethanol were mixed evenly to obtain a mixture (the mass concentration of glucose in the mixture was 36 g / L, and the mass ratio of the metal-modified highly active functional lignin catalyst to glucose was 1:2). The mixture was then transferred to a 10 mL microwave reaction flask and placed in a microwave reactor for glucose isomerization reaction, accompanied by magnetic stirring at a stirring rate of 600 rpm. The reaction ended after 0.5 h. Subsequently, the mixture was filtered through a filter membrane, and the filtered solution was subjected to liquid chromatography to determine the product and calculate the fructose yield.

[0078] The liquid chromatography conditions were as follows: the chromatographic column was Shodex SH1011, the mobile phase was 0.5 ml / min sulfuric acid solution (5 mM), the column temperature was 50 ℃, the injection volume was 10 uL, the glucose and fructose detector was a differential detector, and the detector temperature was 35 ℃.

[0079] The final fructose yield was 57.6%, and the glucose conversion rate was 81.5%.

[0080] The formulas for calculating the glucose conversion rate and fructose yield are as follows:

[0081] Glucose conversion rate (%) = (Concentration of glucose after reaction / Initial concentration of glucose) × 100%

[0082] Fructose yield (%) = fructose production (mol) / glucose units (mol) × 100%.

[0083] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent.

Claims

1. A method for preparing metal-modified functional lignin, characterized by, The method comprises the following steps: Step S1, treating lignin by a chemical oxidation method to obtain functional lignin; Step S2, mechanically ball-milling the functional lignin obtained in step S1 and metal acetate; Step S3, cleaning the material obtained in step S2 with ultrapure water, and vacuum drying to obtain metal-modified functional lignin material; In step S1, the oxidizing agent used in the chemical oxidation method is one or more of hydrogen peroxide, concentrated sulfuric acid and nitric acid; the lignin is alkali lignin, sodium lignosulfonate or lignin extracted from biomass; In step S1, the mass ratio of lignin to oxidizing agent is 1:1-1:5; In step S2, the metal acetate is aluminum acetate, iron acetate, magnesium acetate or tin acetate; In step S2, the mass molar ratio of functional lignin powder to metal acetate is 1g:0.5mol-1g:2mol.

2. Metal-modified functional lignin material prepared by the method according to claim 1.

3. Application of the metal-modified functional lignin material according to claim 2 in preparing fructose from glucose isomerization.

4. Use according to claim 3, characterized in that, The application specifically comprises: Glucose is added to ethanol to configure a reaction solution with a substrate concentration of 5-100 g / L, the metal-modified functional lignin material is used as a catalyst, heating is performed in a microwave reaction device, after the reaction, the upper liquid is taken out for dilution, qualitative and quantitative analysis is performed by using ultra-high performance liquid chromatography, and the metal-modified functional lignin catalyst catalyzes the isomerization of glucose into fructose and its derivatives 5-hydroxymethylfurfural and 5-ethoxymethylfurfural.

5. The application according to claim 4, the mass ratio of the catalyst to glucose is 1:1.5-1:10; the heating temperature is 40-160℃, and the heating time is 0.1-8 h.

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