Synthesis method of green lignin carbon-based solid acid catalyst

Abstract

The invention belongs to the technical field of green synthesis and sustainable chemical engineering, and discloses a synthesis method of a lignin carbon-based solid acid catalyst. The preparation method comprises the following steps: firstly, constructing a three-dimensional carbon skeleton structure system through interaction of sodium lignin sulfonate, ammonium sulfate and sodium sulfanilate in a water phase; a formed carbon skeleton structure is reserved through a freeze drying effect; then, putting the carbon-containing precursor into a tubular furnace, and carbonizing at a certain temperature; the lignin carbon-based material is obtained. And finally, putting the lignin carbon-based material into dilute sulphuric acid, stirring and soaking for a period of time to obtain the lignin carbon-based solid acid catalyst. The method is low in carbonization temperature, a carbon source is a by-product in pulping and papermaking industry, and raw materials are cheap and easily available; and the used sulfuric acid is low in concentration and small in dosage. And meanwhile, extra energy consumption is not generated in the room-temperature and normal-pressure environment, and the requirement of the dilute acid treatment process on equipment is greatly improved. Therefore, the method has a relatively high application value.

Description

Technical Field

[0001] The invention belongs to the technical field of green synthesis and sustainable chemical engineering, and particularly relates to a method for synthesizing a green lignin carbon-based solid acid catalyst. Background Art

[0002] Carbon solid acid catalysts are a type of heterogeneous catalyst. Compared with liquid homogeneous catalysts and heterogeneous catalysts such as zeolites, resins and metal oxides, carbon solid acid catalysts have the advantages of high reaction activity, rich surface functional groups, adjustable pore structure, recyclability and excellent thermal stability. In recent years, carbon solid acid catalysts have shown excellent results in the dehydration of fructose to 5-hydroxymethylfurfural. This type of solid acid catalyst is mainly used in The -SO3H group at the acid site is mainly used as a proton acid in the catalytic process. + Ionic protonation of the -OH groups in fructose molecules enables continuous dehydration of fructose, ultimately yielding 5-hydroxymethylfurfural. Traditional carbon solid acid catalyst preparation involves two steps: first, activation of biomass waste at very high carbonization temperatures due to the high decomposition temperatures of traditional chemical activators such as ZnCl2, KOH, and NaCl; and then sulfonation in a concentrated sulfuric acid environment at 130-180°C. Consequently, traditional carbon solid acid catalysts suffer from high energy consumption for carbonization and sulfonation, as well as high sulfuric acid requirements. Therefore, finding a low-temperature and low-acid preparation method for carbon solid acids is crucial, as it is crucial for energy conservation and environmental protection.

[0003] At present, the preparation method of green carbon-based solid acid is still in the exploratory stage. The green carbon solid acid preparation method that has been reported is mainly to replace concentrated sulfuric acid with other organic acids for treatment, but there is still a problem of too high carbonization temperature (≥600℃), and only weakly acidic -COOH and phenol-OH groups exist in the structure, lacking strongly acidic -SO3H groups. In addition, the mainstream method of replacing sulfonation reaction is to use organic acid (p-toluenesulfonic acid, etc.) for hydrothermal treatment. Although the use of concentrated sulfuric acid is avoided, the energy consumption of the hydrothermal process is still huge, and the problem of the pyrolysis temperature of the carbon precursor has not been solved. Therefore, it is very important to find a green carbon-based solid acid synthesis method, which requires not only the ability to construct the pore structure of the carbon skeleton under low-temperature carbonization, but also to replace the high-energy sulfonation reaction.

[0004] Based on this, this patent proposes a green, low-cost, low-energy and low-acid preparation method for lignin carbon-based solid acid, aiming to improve the unsustainable problems such as high energy consumption and high acid usage in the preparation process of carbon solid acid, and provide strong support for the development of low-energy, biomass-friendly carbon-based catalyst technology. Summary of the Invention

[0005] The purpose of the present invention is to provide a green synthesis method of lignin carbon-based solid acid catalyst to solve the problems of high energy consumption and high acid dosage of traditional carbon-based solid acid that rely on high temperature carbonization activation and sulfonation.

[0006] The invention is realized through the following technical solutions:

[0007] A method for synthesizing a green lignin carbon-based solid acid catalyst comprises the following steps:

[0008] (1) Mixing sodium lignin sulfonate, ammonium sulfate, sodium p-aminobenzenesulfonate and water and completely dissolving them;

[0009] (2) freezing the mixed solution, and then freeze-drying the completely frozen carbon source to obtain a precursor;

[0010] (3) carbonizing the precursor at a set temperature, washing and drying it, and then passing it through an 80-mesh sieve to obtain a lignin carbon-based material;

[0011] (4) The obtained lignin carbon-based material is placed in dilute sulfuric acid, magnetically stirred, and then washed and dried to obtain a lignin carbon-based solid acid catalyst.

[0012] Furthermore, the mass ratio of sodium lignin sulfonate, sodium p-aminobenzenesulfonate and ammonium sulfate described in step (1) is between 8:2:2 and 2:8:2.

[0013] Furthermore, the mass of the water in step (1) is 3 to 15 times the sum of the mass of sodium lignin sulfonate and sodium p-aminobenzenesulfonate.

[0014] Furthermore, the freezing temperature in step (2) is -60°C;

[0015] The freeze-drying temperature was -50°C and the freeze-drying time was 72 h.

[0016] Furthermore, the carbonization gas atmosphere in step (3) is nitrogen.

[0017] Furthermore, the carbonization temperature in step (3) is 250-400° C., and the carbonization time is 1-2 h.

[0018] Furthermore, the washing in step (3) is first washing in 10 wt % dilute hydrochloric acid, and then washing with pure water and ethanol until the pH of the washing solution is 7.

[0019] Furthermore, the concentration of the dilute sulfuric acid in step (4) is 1 mol / L, the temperature is controlled to be room temperature, the pressure is normal pressure, and the stirring time is 2 to 10 hours.

[0020] Furthermore, the washing in step (4) is performed with pure water until no white precipitate is generated when BaCl2 is added.

[0021] Furthermore, the drying temperature and time in step (3) and step (4) are controlled to be the same, namely, the temperature is 105° C. and the time is 4 to 8 hours.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] 1. The raw material precursors used in the present invention are mainly sodium lignin sulfonate, which is a by-product of the pulp and paper industry and has low cost; sodium p-aminobenzenesulfonate and ammonium sulfate are mainly used in the fertilizer industry and are relatively cheap.

[0024] 2. The present invention adopts a low-temperature incomplete carbonization method to prepare lignin carbon-based solid acid, which greatly reduces the energy consumption required for carbonization; at the same time, it can construct a macroporous carbon skeleton structure at a lower carbonization temperature.

[0025] 3. The macroporous carbon skeleton structure constructed by the present invention avoids the use of traditional activators, overcoming the shortcomings of traditional activators requiring large amounts of activators and high activation temperatures.

[0026] 4. The present invention replaces high-temperature sulfonation in a concentrated sulfuric acid environment with proton exchange at room temperature and normal pressure, completely saving the energy consumption required for sulfonation, reducing the generation of a large amount of acidic waste liquid, and lowering the requirements for production equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a typical SEM image of lignin carbon solid acid;

[0028] Figure 2 This is the infrared spectrum of a typical lignin carbon solid acid. DETAILED DESCRIPTION

[0029] The present invention is described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited to the specific embodiments. Other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the technical essence of the present invention should be considered as equivalent replacement methods and fall within the scope of protection of the technical solution of the present invention.

[0030] Example 1

[0031] A method for synthesizing a green lignin carbon-based solid acid catalyst comprises the following steps:

[0032] (1) Add 4g of sodium lignin sulfonate, 1g of sodium p-aminobenzenesulfonate and 1g of ammonium sulfate to a beaker, add 15g of pure water and stir evenly;

[0033] (2) The obtained mixed solution was placed in a refrigerator at -60°C for 1 day, and then freeze-dried at -50°C for 3 days to obtain a lignin carbon precursor.

[0034] (3) placing the lignin carbon precursor in a tube furnace, repeatedly evacuating the vacuum for 3 times, carbonizing the precursor at 350 °C for 1 h in a nitrogen atmosphere, and then passing through an 80-mesh sieve to obtain a lignin carbon material;

[0035] (4) The obtained lignin carbon material was washed in 10 wt% dilute hydrochloric acid, then washed with pure water and ethanol until pH = 7, and then dried in an oven at 105 ° C for 12 h. The dried lignin carbon material was proton exchanged in 1 mol / L dilute sulfuric acid at a ratio of 1 g:50 mL to obtain a lignin carbon-based solid acid;

[0036] (5) The obtained lignin carbon-based solid acid was reacted in a reaction system of 1 g fructose, 0.05 g lignin carbon-based solid acid, 4 mL DMSO (dimethyl sulfoxide) and 1 mL water at a temperature of 170° C. for 1 h.

[0037] Example 2

[0038] A method for synthesizing a green lignin carbon-based solid acid catalyst comprises the following steps:

[0039] (1) Add 2g of sodium lignin sulfonate, 3g of sodium p-aminobenzenesulfonate and 1g of ammonium sulfate to a beaker, add 25g of pure water and stir evenly;

[0040] (2) freezing the obtained mixture in a refrigerator at -60°C for 1 day, and then freeze-drying it at -50°C for 3 days to obtain a lignin carbon precursor;

[0041] (3) placing the lignin carbon precursor in a tube furnace, repeatedly evacuating the vacuum for 3 times, carbonizing the precursor at 300 °C for 1 h in a nitrogen atmosphere, and then passing through an 80-mesh sieve to obtain a lignin carbon material;

[0042] (4) The obtained lignin carbon material was washed in 10 wt% dilute hydrochloric acid, then washed with pure water and ethanol until pH = 7, and then dried in an oven at 105 ° C for 12 h. The dried lignin carbon material was proton exchanged in 1 mol / L dilute sulfuric acid at a ratio of 1 g:50 mL to obtain a lignin carbon-based solid acid;

[0043] (5) The obtained lignin carbon-based solid acid was reacted in a reaction system of 1 g fructose, 0.05 g lignin carbon-based solid acid, 4 mL DMSO and 1 mL water at a temperature of 170° C. for 1 h.

[0044] Example 3

[0045] A method for synthesizing a green lignin carbon-based solid acid catalyst comprises the following steps:

[0046] (1) Add 2.5 g of sodium lignin sulfonate, 2.5 g of sodium p-aminobenzenesulfonate, and 1 g of ammonium sulfate into a beaker, add 25 g of pure water, and stir evenly;

[0047] (2) freezing the obtained mixture in a refrigerator at -60°C for 1 day, and then freeze-drying it at -50°C for 3 days to obtain a lignin carbon precursor;

[0048] (3) placing the lignin carbon precursor in a tube furnace, repeatedly evacuating the tube furnace three times, carbonizing the precursor at 350 °C for 1 h in a nitrogen atmosphere, and then passing through an 80-mesh sieve to obtain a lignin carbon material;

[0049] (4) The obtained lignin carbon material was washed in 10 wt% dilute hydrochloric acid, then washed with pure water and ethanol until pH = 7, and then dried in an oven at 105 ° C for 12 h. The dried lignin carbon material was proton exchanged in 1 mol / L dilute sulfuric acid at a ratio of 1 g:50 mL to obtain a lignin carbon-based solid acid;

[0050] (5) The obtained lignin carbon-based solid acid was reacted in a reaction system of 1 g fructose, 0.05 g lignin carbon-based solid acid, and 5 mL DMSO at a temperature of 170° C. for 1 h.

[0051] Example 4

[0052] A method for synthesizing a green lignin carbon-based solid acid catalyst comprises the following steps:

[0053] (1) Add 2.5g of sodium lignin sulfonate, 2.5g of sodium p-aminobenzenesulfonate and 1g of ammonium sulfate into a beaker, add 25% pure water and stir evenly;

[0054] (2) freezing the obtained mixture in a refrigerator at -60°C for 1 day, and then freeze-drying it at -50°C for 3 days to obtain a lignin carbon precursor;

[0055] (3) placing the lignin carbon precursor in a tube furnace, repeatedly evacuating the vacuum for 3 times, carbonizing the precursor at 300 °C for 2 h in a nitrogen atmosphere, and then passing through an 80-mesh sieve to obtain a lignin carbon material;

[0056] (4) The obtained lignin carbon material was washed in 10 wt% dilute hydrochloric acid, then washed with pure water and ethanol until pH = 7, and then dried in an oven at 105 ° C for 12 h. The dried lignin carbon material was proton exchanged in 1 mol / L dilute sulfuric acid at a ratio of 1 g:50 mL to obtain a lignin carbon-based solid acid;

[0057] (5) The obtained lignin carbon-based solid acid was reacted in a reaction system of 1 g fructose, 0.05 g lignin carbon-based solid acid, 4 mL DMSO and 1 mL water at a temperature of 160° C. for 1 h.

[0058] Example 5

[0059] A method for synthesizing a green lignin carbon-based solid acid catalyst comprises the following steps:

[0060] (1) Add 3g of sodium lignin sulfonate, 2g of sodium p-aminobenzenesulfonate and 1g of ammonium sulfate into a beaker, add 50ml of pure water and stir evenly;

[0061] (2) freezing the obtained mixture in a refrigerator at -60°C for 1 day, and then freeze-drying it at -50°C for 3 days to obtain a lignin carbon precursor;

[0062] (3) placing the lignin carbon precursor in a tube furnace, repeatedly evacuating the vacuum for 3 times, carbonizing the precursor at 350 °C for 1 h in a nitrogen atmosphere, and then passing through an 80-mesh sieve to obtain a lignin carbon material;

[0063] (4) The obtained lignin carbon material was washed in 10 wt% dilute hydrochloric acid, then washed with pure water and ethanol until pH = 7, and then dried in an oven at 105 ° C for 12 h. The dried lignin carbon material was proton exchanged in 1 mol / L dilute sulfuric acid at a ratio of 1 g:50 mL to obtain a lignin carbon-based solid acid;

[0064] (5) The obtained lignin carbon-based solid acid was reacted in a reaction system of 1 g fructose, 0.05 g lignin carbon-based solid acid, 3 mL DMSO and 2 mL water at a temperature of 170° C. for 1 h.

[0065] Comparative Example 1

[0066] In the comparative example, no lignin carbon-based solid acid catalyst was added, and only 1 g of fructose, 4 mL of DMSO and 1 mL of water were added to the system for reaction for 1 h at a reaction temperature of 170°C.

[0067] Table 1 The yield and conversion rate of fructose into 5-hydroxymethylfurfural catalyzed by the prepared lignin carbon-based solid acid

[0068] Example Fructose conversion rate (%) 5-Hydroxymethylfurfural yield (%) Example 1 98.42 77.68 Example 2 95.37 74.68 Example 3 99.26 83.48 Example 4 88.67 68.28 Example 5 96.73 73.58 Comparative Example 1 54.33 37.42

[0069] It can be seen from Table 1 above that the lignin carbon-based solid acid prepared by the method of the present invention can effectively catalyze the conversion of fructose into 5-hydroxymethylfurfural, and the conversion rate of fructose is high.

[0070] Figure 1This is a typical SEM image of lignin carbon solid acid. The spectrum shows the pore skeleton structure of the prepared lignin carbon-based solid acid, indicating that sodium lignin sulfonate, sodium p-aminobenzenesulfonate and ammonium sulfate form a three-dimensional macroporous structure.

[0071] Figure 2 This is a typical infrared spectrum of lignin carbon solid acid, which shows characteristic peaks of -OH, -COOH and -SO3H functional groups, indicating that the structure of lignin carbon-based solid acid has weak acid and strong acid catalytic reaction sites.

[0072] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for synthesizing a green lignin carbon-based solid acid catalyst, characterized in that: The steps include: (1) Mixing sodium lignin sulfonate, ammonium sulfate, sodium p-aminobenzenesulfonate and water and completely dissolving them; (2) freezing the mixed solution, and then freeze-drying the completely frozen carbon source to obtain a precursor; (3) carbonizing the precursor at a set temperature, washing and drying it, and then passing it through an 80-mesh sieve to obtain a lignin carbon-based material; (4) The obtained lignin carbon-based material is placed in dilute sulfuric acid, magnetically stirred, and then washed and dried to obtain a lignin carbon-based solid acid catalyst.

2. The method for synthesizing a green lignin carbon-based solid acid catalyst according to claim 1, characterized in that: The mass ratio of sodium lignin sulfonate, sodium p-aminobenzenesulfonate and ammonium sulfate described in step (1) is between 8:2:2 and 2:8:

2.

3. The method for synthesizing a green lignin carbon-based solid acid catalyst according to claim 1, characterized in that: The mass of the water in step (1) is 3 to 15 times the mass of the sodium lignin sulfonate and the sodium p-aminobenzenesulfonate.

4. The method for synthesizing a green lignin carbon-based solid acid catalyst according to claim 1, characterized in that: The freezing temperature in step (2) is -60°C; The freeze-drying temperature was -50°C and the freeze-drying time was 72 h.

5. The method for synthesizing a green lignin carbon-based solid acid catalyst according to claim 1, characterized in that: The carbonization gas atmosphere in step (3) is nitrogen.

6. The method for synthesizing a green lignin carbon-based solid acid catalyst according to claim 1, characterized in that: The carbonization temperature in step (3) is 250-400° C., and the carbonization time is 1-2 hours.

7. The method for synthesizing a green lignin carbon-based solid acid catalyst according to claim 1, characterized in that: The washing in step (3) is first washing in 10 wt % dilute hydrochloric acid, and then washing with pure water and ethanol until the pH of the washing solution is 7.

8. The method for synthesizing a green lignin carbon-based solid acid catalyst according to claim 1, characterized in that: The concentration of the dilute sulfuric acid in step (4) is 1 mol / L, the temperature is controlled to be room temperature, the pressure is normal pressure, and the stirring time is 2 to 10 hours.

9. The method for synthesizing a green lignin carbon-based solid acid catalyst according to claim 1, characterized in that: The washing in step (4) is performed with pure water until no white precipitate is produced when BaCl2 is added.

10. The method for synthesizing a green lignin carbon-based solid acid catalyst according to claim 1, characterized in that: The drying temperature and time in step (3) and step (4) are controlled to be the same, namely, the temperature is 105° C. and the time is 4 to 8 hours.

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