Non-metal nitrogen-doped lignin-based porous carbon material, preparation method thereof and application of non-metal nitrogen-doped lignin-based porous carbon material in catalyzing aldehyde ammonia oxidation to synthesize nitrile

Abstract

The invention discloses a non-metal nitrogen-doped lignin-based porous carbon material, a preparation method thereof and application of the non-metal nitrogen-doped lignin-based porous carbon material in catalyzing aldehyde ammoxidation to synthesize nitrile. According to the technical scheme, sodium lignin sulfonate, melamine and potassium hydroxide are sufficiently mixed through ball milling, powder obtained after ball milling is put into a tubular furnace to be pyrolyzed, the pyrolyzed powder is sufficiently ground through a mortar and then subjected to ultrasonic cleaning and centrifugation, obtained solids are washed with methyl alcohol, centrifuged again and dried, and the modified sodium lignin sulfonate is obtained. The non-metal nitrogen-doped lignin-based porous carbon material is obtained; the prepared catalyst is free of metal and high in activity, selectivity and applicability, nitrile can be prepared by catalyzing aldehyde through a one-pot method at high conversion rate and high selectivity under the mild condition, the formed nitrile cannot be further converted into amide, the catalyst has good tolerance to other oxidizable groups, the catalyst has huge potential, and the method is suitable for industrial production. The green, cheap and efficient catalyst is expected to be applied to large-scale industrial production in the future.

Description

Technical Field

[0001] The present invention relates to the field of energy chemistry, and particularly to a preparation method of a non-metallic nitrogen-doped lignin-based porous carbon material and its application in the synthesis of nitriles by aldehyde-ammonia-oxygen. Background Art

[0002] Nitrile compounds are essential intermediates due to their versatile reactivity and unique properties, and are widely used in the synthesis of pharmaceuticals, pesticides, dyes, polymers, and other fine chemicals. There are many traditional methods for synthesizing nitrile compounds, including the cyanation of organic halides, the amination oxidation of toluene, the dehydration of amides or oximes, and the oxidation of amines. However, these traditional methods often have obvious drawbacks. For example, the use of toxic organic solvents, dangerous cyanides or hydrogen cyanide as starting materials generates difficult-to-manage hazardous wastes, posing serious environmental and safety risks. In addition, many of these methods require harsh reaction conditions, such as elevated temperature and pressure, which limits their practicality and sustainability. Therefore, in recent years, the green synthesis and sustainable development of nitrile compounds have received increasing attention, aiming to address these challenges while minimizing environmental impact and pollution.

[0003] In recent years, a cyanide-free method for synthesizing nitriles has attracted wide attention. This method uses ammonia water as the nitrogen source and oxygen as the oxidant to convert alcohols or aldehydes into nitriles. This method not only avoids the use of highly toxic cyanides but also uses oxygen as a green and sustainable oxidant, with water as the only by-product of the reaction.

[0004] In the early studies on the synthesis of nitriles by the oxidation of alcohols or aldehydes, common oxidants and solvents such as I2 and (Bu4N)2S2O8 generated a large amount of waste and caused environmental damage. In addition, several homogeneous catalysts with excellent catalytic performance, such as the nitro / NOx system and modified TEMPOs, have been developed. However, the use of homogeneous catalysts brings additional challenges, including product separation and catalyst recycling, which remain major drawbacks of homogeneous catalysis. These limitations have prompted a shift towards exploring recyclable heterogeneous catalysts, which provide more practical and sustainable solutions.

[0005] In the past decade, a variety of metal-based heterogeneous catalysts have been reported for the oxidative conversion of alcohols or aldehydes to nitriles, such as Ru, Ag, Co, Fe, and Cu. Although these metal-based catalysts have a wide range of properties, they still have their inherent disadvantages and limitations. For example, high cost (a key factor in industrial-scale production, metal-based catalysts are usually expensive), catalyst deactivation (impurities in the reaction system can deactivate metal catalysts, and in oxidation reactions, the conversion of metals from low oxidation states to high oxidation states can change catalytic activity), complex recycling and reuse processes (in the recovery process of metal catalysts, drying after washing may require a vacuum environment, and the recovered catalysts sometimes may need to be reduced and reactivated), increased side reactions (the high reactivity of metal-based catalysts often promotes unnecessary side reactions, reducing the selectivity for the target product), and metal toxicity (the residual metal content must be strictly controlled, especially when synthesizing nitrile drug intermediates).

[0006] Given these limitations, non-metal catalysts are a very promising and underdeveloped alternative with great innovation potential. Summary of the Invention

[0007] To overcome the problems existing in the prior art, the present invention provides a method for preparing a non-metal nitrogen-doped lignin-based porous carbon material. In this method, sodium lignosulfonate, melamine, and potassium hydroxide are mixed by a simple ball-milling method and prepared into a non-metal nitrogen-doped lignin-based porous carbon material through high-temperature pyrolysis in a nitrogen atmosphere.

[0008] The second object of the present invention is to provide a non-metal nitrogen-doped lignin-based porous carbon material. This catalyst has no metal elements and can catalytically synthesize nitriles by one-pot oxidation of aldehydes and ammonia under mild conditions. Moreover, the formed nitriles will not be further converted into amides and have good tolerance to other oxidizable groups.

[0009] The second object of the present invention is to provide a method for synthesizing nitriles by the oxidation of aldehydes and ammonia. This method can catalytically prepare nitriles from aldehydes by one-pot method with high conversion rate and high selectivity under mild conditions.

[0010] To achieve the above object, the first technical solution provided by the present invention is as follows: A method for preparing a non-metal nitrogen-doped lignin-based porous carbon material, comprising the following steps: mixing sodium lignosulfonate, melamine, and potassium hydroxide by ball milling, putting the milled powder into a tube furnace for pyrolysis at 600 - 900 °C, grinding the pyrolyzed powder, then performing ultrasonic cleaning and centrifugation, collecting the solid, washing it, and centrifuging it again, and drying to obtain the non-metal nitrogen-doped lignin-based porous carbon material.

[0011] Further, in the preparation method of the above non-metal nitrogen-doped lignin-based porous carbon material, the mass ratio of sodium lignosulfonate, melamine, and potassium hydroxide is 4:3:1.3.

[0012] Further, in the preparation method of the above non-metal nitrogen-doped lignin-based porous carbon material, the rotation speed of ball milling is 300 - 600 rpm, and the ball milling time is 6 - 10 h.

[0013] Further, the ball milling adopts forward and reverse intermittent ball milling. Specifically, for every 30 min of ball milling, it pauses for 5 min, and then changes the rotation direction to continue ball milling for 30 min.

[0014] Further, in the preparation method of the above non-metal nitrogen-doped lignin-based porous carbon material, the pyrolysis is carried out in a nitrogen gas atmosphere. The temperature is raised to 700 - 900 °C at a heating rate of 4 - 6 °C / min, held at this temperature for 60 min, and finally cooled naturally. Further, in the preparation method of the above non-metal nitrogen-doped lignin-based porous carbon material, the washing is carried out using methanol.

[0015] In some specific embodiments of the present invention, the powder after pyrolysis is fully ground using a mortar, then subjected to ultrasonic cleaning and centrifugation. The obtained solid is washed with methanol and centrifuged again. The rotation speed of the centrifugation is 9000 - 12000 rpm, and the centrifugation time is 2 - 3 min.

[0016] The second technical solution of the present invention is as follows: A non-metal nitrogen-doped lignin-based porous carbon material obtained by the preparation method of the non-metal nitrogen-doped lignin-based porous carbon material described in the first technical solution.

[0017] The third aspect of the present invention provides the application of the metal-free nitrogen-doped lignin-based porous carbon material in the synthesis of nitriles by aldehyde-ammonia oxidation.

[0018] Another technical solution of the present invention is to provide a method for synthesizing nitriles by aldehyde-ammonia oxidation, which includes the following steps: adding an aldehyde compound and a nitrogen-doped lignin-based porous carbon material into a reaction kettle, then successively adding a solvent and ammonia water, and introducing oxygen so that the final pressure in the reaction kettle is 0.6 - 1 MPa, and reacting at 60 - 80 °C for 1 - 12 h to obtain a nitrile compound.

[0019] Further, in the above method for synthesizing nitriles by aldehyde-ammonia oxidation, the aldehyde compound includes at least one of benzaldehyde, 4-methylbenzaldehyde, 4-ethylbenzaldehyde, 4-hydroxybenzaldehyde, 4-fluorobenzaldehyde, 4-chlorobenzaldehyde, 4-bromobenzaldehyde, 4-iodobenzaldehyde, 4-methoxybenzaldehyde, 4-ethoxybenzaldehyde, terephthalaldehyde, 4-biphenylaldehyde, and 2-naphthaldehyde; the solvent is acetonitrile.

[0020] Furthermore, in the above method for synthesizing nitrile by ammoxidation of aldehyde, the dosage ratio of the aldehyde compound, nitrogen-doped lignin-based porous carbon material, and ammonia water is 0.5 mmol: 100 mg: 200 μL; the concentration of the ammonia water is 25 - 30 wt%.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The present invention provides a preparation method of a metal-free nitrogen-doped lignin-based porous carbon material catalyst for synthesizing nitrile by ammoxidation of aldehyde. The catalyst is prepared by simply mixing sodium lignosulfonate, melamine, and potassium hydroxide by ball milling and then pyrolyzing at high temperature in a nitrogen atmosphere. The raw materials are green, cheap, and sustainable, the preparation period is short, and it has the advantages of economy, greenness, high efficiency, and low cost, and is expected to be applied in large-scale industrial production; 2. In the present invention, potassium hydroxide is used as an activator to activate the lignin-based carbon material, and a catalyst with a high BET specific surface area and pores is synthesized, exposing more active sites, and significantly improving the catalytic activity of the oxidation nitrilation of benzaldehyde derivatives to generate the corresponding nitriles; 3. The catalyst provided by the present invention contains no metal elements, has low cost, good stability, is easy to recycle and reuse, and also has high activity, selectivity, and applicability. The formed nitrile will not be further converted into amide and has good tolerance to other oxidizable groups; moreover, it can be reused after the reaction, and the catalyst can be recycled through simple operations: centrifugal separation, washing, and drying; after five reactions, the ammoxidation effect has no significant change, and it has great application prospects; 4. The synthesis route provided by the present invention directly prepares nitrile by a one-pot method of aldehyde and ammonia under oxygen conditions, uses ammonia water as a nitrogen source, and oxygen as a green oxidant. The only by-product of the reaction is water. The synthesis route avoids the use of cyanide, is environmentally friendly and pollution-free, and has green sustainability; 5. The synthesis route provided by the present invention does not produce by-products such as benzamide and benzoic acid, and no further oxidation occurs, having high selectivity and conversion rate; moreover, it can have excellent ammoxidation catalytic effects on various derivatives of benzaldehyde under different conditions and has wide applicability. Description of the Drawings

[0022] Figure 1 SEM image of CN-900-300 in Example 4; Figure 2 TEM image of CN-900-300 in Example 4; Figure 3 XPS full spectrum of CN-900-300 in Example 4; Figure 4XRD patterns of the catalysts synthesized at different calcination temperatures in Examples 1-4; Figure 5 Raman spectra of the catalysts synthesized at different calcination temperatures in Examples 1-4; Figure 6 N2 adsorption-desorption isotherm of CN-900-300 in Example 4; Figure 7 Pore size distribution diagram of CN-900-300 in Example 4; Figure 8 Comparison chart of benzonitrile yields of catalysts at different pyrolysis temperatures; Figure 9 Comparison chart of benzonitrile yields at different reaction times; Figure 10 Comparison chart of benzonitrile yields at different oxygen pressures; Figure 11 Comparison chart of benzonitrile yields at different ball milling speeds; Figure 12 Comparison chart of benzonitrile yields of CN-900-300 in five-cycle reactions. Detailed implementation manners

[0023] The following further describes the detailed implementation manners of the present invention. It should be noted here that the description of these implementation manners is for helping to understand the present invention, but does not constitute a limitation to the present invention. In addition, the technical features involved in the following various implementation manners of the present invention can be combined with each other as long as they do not conflict with each other.

[0024] The experimental methods in the following examples are all conventional methods unless otherwise specified, and the test materials used in the following examples can all be obtained through conventional commercial channels unless otherwise specified. Example 1

[0025] Weigh 4.0058 g of sodium lignosulfonate, 3.0018 g of melamine, and 1.3025 g of potassium hydroxide and add them to a planetary ball mill. Set the rotation speed to 300 rpm and perform intermittent ball milling in both forward and reverse directions for 10 h for mixing (intermittent ball milling in both forward and reverse directions means ball milling for 30 min each time, pausing for 5 min, and then changing the rotation direction to continue ball milling for 30 min, repeating in turn until the total ball milling time is 10 h), and collect the powder after ball milling;

[0026] The milled powder mentioned above was loaded into an alumina crucible, and the crucible was placed in a tube furnace. Nitrogen was introduced, and the heating program was set as follows: the heating rate was 5 °C / min, the pyrolysis temperature was 600 °C, and the holding time was 60 min. Pyrolysis was carried out, and after the pyrolysis was completed, the temperature decreased naturally. After waiting for the temperature to drop to room temperature, the pyrolyzed black powder was collected. The pyrolyzed powder was thoroughly ground using a mortar and then put into a beaker. Deionized water was added to the scale of 500 ml, and ultrasonic cleaning was carried out for 90 min and centrifuged (the rotation speed of the centrifugation was 9000 rpm, and the centrifugation time was 3 min), and then filtered. The obtained solid was washed with methanol and centrifuged again, and vacuum dried at 80 °C for 10 h, thus obtaining a metal-free nitrogen-doped lignin-based porous carbon material. The obtained product was named CN-600-300.

[0027] Application Example 1 The catalyst prepared in Example 1 was used in the ammoxidation reaction of benzaldehyde. 0.5 mmol of benzaldehyde, 3 mL of acetonitrile, 100 mg of CN-600, 200 μL of ammonia (the concentration of ammonia water was 28 wt%), and 0.8 MPa of oxygen (the purity of oxygen was 99.99%) were added to a 25 mL reaction kettle for reaction. Under magnetic stirring, the reaction temperature was 60 °C, and it was maintained for 5 h, and the yield of benzonitrile was 3%. Example 2

[0028] 4.0023 g of sodium lignosulfonate, 3.0121 g of melamine, and 1.3019 g of potassium hydroxide were weighed and added to a planetary ball mill. The rotation speed was set to 300 rpm, and positive and negative rotation intermittent ball milling was carried out for 10 h for mixing (positive and negative rotation intermittent ball milling was that for every 30 min of ball milling, it was paused for 5 min, and then the rotation direction was changed to continue ball milling for 30 min, and this was repeated in turn until the total ball milling time was 10 h), and the powder after ball milling was collected; The milled powder mentioned above was loaded into an alumina crucible, and the crucible was placed in a tube furnace. Nitrogen was introduced, and the heating program was set as follows: the heating rate was 5 °C / min, the pyrolysis temperature was 700 °C, and the holding time was 60 min. Pyrolysis was carried out, and after the pyrolysis was completed, the temperature decreased naturally. After waiting for the temperature to drop to room temperature, the pyrolyzed black powder was collected. The pyrolyzed powder was thoroughly ground using a mortar and then put into a beaker. Deionized water was added to the scale of 500 ml, and ultrasonic cleaning was carried out for 90 min and centrifuged (the rotation speed of the centrifugation was 12000 rpm, and the centrifugation time was 2 min), and then filtered. The obtained solid was washed with methanol and centrifuged again, and vacuum dried at 80 °C for 10 h, thus obtaining a metal-free nitrogen-doped lignin-based porous carbon material. The obtained product was named CN-700-300.

[0029] Application Example 2 The catalyst prepared in Example 1 was used in the ammoxidation reaction of benzaldehyde. 0.5 mmol of benzaldehyde, 3 mL of acetonitrile, 100 mg of CN-700, 200 μL of ammonia (ammonia water concentration is 28 wt%), and 0.8 MPa of oxygen (oxygen is 99.99%) were added to a 25 mL reaction kettle for reaction. Under magnetic stirring, the reaction temperature was 60 °C and maintained for 5 h, and the yield of benzonitrile was 16%. Example 3

[0030] Weigh 4.0031 g of sodium lignosulfonate, 3.0023 g of melamine, and 1.3011 g of potassium hydroxide and add them to a planetary mill. Set the rotation speed to 300 rpm and perform intermittent ball milling in forward and reverse directions for 10 h for mixing (intermittent ball milling in forward and reverse directions means ball milling for 30 min each time, pausing for 5 min, then changing the rotation direction and continuing ball milling for 30 min, repeating in turn until the total ball milling time is 10 h), and collect the powder after ball milling; Put the powder after the above ball milling into an alumina crucible, place the crucible in a tube furnace, introduce nitrogen, and set the heating program: the heating rate is 5 °C / min, the pyrolysis temperature is 800 °C, and the holding time is 60 min for pyrolysis. After the pyrolysis is completed, it is cooled naturally. Wait until the temperature drops to room temperature and then collect the black powder after pyrolysis. The powder after pyrolysis is fully ground in a mortar and then put into a beaker, add deionized water to the scale of 500 ml, perform ultrasonic cleaning for 90 min and centrifuge (the rotation speed of the centrifuge is 11000 rpm and the centrifugation time is 3 min), filter, wash the obtained solid with methanol and centrifuge again, and vacuum dry at 80 °C for 10 h to obtain a metal-free nitrogen-doped lignin-based porous carbon material. The obtained product is named CN-800-300.

[0031] Application Example 3 The catalyst prepared in Example 3 was used in the ammoxidation reaction of benzaldehyde. 0.5 mmol of benzaldehyde, 3 mL of acetonitrile, 100 mg of CN-800, 200 μL of ammonia (ammonia water concentration is 28 wt%), and 0.8 MPa of oxygen (oxygen is 99.99%) were added to a 25 mL reaction kettle for reaction. Under magnetic stirring, the reaction temperature was 60 °C and maintained for 5 h, and the yield of benzonitrile was 84%. Example 4

[0032] Weigh 4.0016 g of sodium lignosulfonate, 3.0101 g of melamine, and 1.3045 g of potassium hydroxide and add them to a planetary mill. Set the rotation speed to 300 rpm and perform intermittent ball milling in forward and reverse directions for 10 h for mixing (intermittent ball milling in forward and reverse directions means ball milling for 30 min each time, pausing for 5 min, then changing the rotation direction and continuing ball milling for 30 min, repeating in turn until the total ball milling time is 10 h), and collect the powder after ball milling; Load the ball-milled powder into an alumina crucible, place the crucible in a tube furnace, introduce nitrogen, and set the heating program: the heating rate is 5 °C / min, the pyrolysis temperature is 900 °C, and the holding time is 60 min. Then carry out pyrolysis and let it cool down naturally after pyrolysis. Wait until the temperature drops to room temperature and collect the pyrolyzed black powder. The pyrolyzed powder is thoroughly ground in a mortar and then put into a beaker, add deionized water to the scale of 500 ml, carry out ultrasonic cleaning for 90 min and centrifuge (the rotation speed of the centrifuge is 10,000 rpm and the centrifugation time is 3 min), filter. The obtained solid is washed with methanol and centrifuged again, and vacuum dried at 80 °C for 10 h to obtain a metal-free nitrogen-doped lignin-based porous carbon material, and the obtained product is named CN-900-300.

[0033] To prove the physicochemical properties of the metal-free nitrogen-doped lignin-based porous carbon material provided by this application, the following are the detection spectra of CN-900-300 prepared in this application. The SEM image is referred to Figure 1 , and it can be seen through Figure 1 that the material has a porous and flaky structure; the TEM image is referred to Figure 2 , and it can be seen through Figure 2 that the material has a rich porosity and the morphology presents an ultrathin nanosheet structure; the XPS full-spectrum image is referred to Figure 3 , and it can be confirmed through Figure 3 the presence of C, N, and O in CN-900-300. The weak signals of S, Na, and K indicate that they are removed during the pyrolysis process and the washing process, proving that the catalyst is a non-metallic carbon material; the nitrogen adsorption-desorption curve is referred to Figure 6 , and it can be obtained through Figure 6 that the adsorption-desorption isotherm of CN-900-300 shows the information of a composite type of type I and type IV, proving the simultaneous presence of micropores and mesopores in the material; the pore size distribution map is referred to Figure 7 , and it can be seen through Figure 7 that the micropore diameters are 0.80 nm and 1.48 nm respectively, and the mesopore diameter is 2.52 nm.

[0034] The XRD patterns of the catalysts synthesized in Examples 1-4 at different calcination temperatures are referred to Figure 4 , and it can be seen through Figure 4 that there is a broad peak at about 25°, which reflects the existence of a graphite-like layered structure in the carbon material.

[0035] The Raman spectra of the catalysts synthesized in Examples 1-4 at different calcination temperatures; refer to Figure 5 , and it can be seen through Figure 5 that as the pyrolysis temperature increases, the ID / IG ratio of the synthesized catalyst decreases, indicating that increasing the pyrolysis temperature can improve the graphitization degree of the catalyst and reduce defects.

[0036] Application Example 4 The catalyst prepared in Example 4 was used in the ammoxidation reaction of benzaldehyde. 0.5 mmol of benzaldehyde, 3 mL of acetonitrile, 100 mg of CN-900-300, 200 μL of ammonia (ammonia water concentration is 28 wt%), and 0.8 MPa of oxygen (oxygen is 99.99%) were added to a 25 mL reaction kettle for reaction. Under magnetic stirring, the reaction temperature was 60 °C and maintained for 5 h, and the yield of benzonitrile was 98%.

[0037] The BET surface areas of the catalysts synthesized at different calcination temperatures in Examples 1-4 are shown in Table 1 below.

[0038] Table 1

[0039] It can be seen from Table 1 that as the pyrolysis temperature increases, the BET specific surface area of the catalyst becomes larger and the change degree is more obvious. CN-800-300 and CN-900-300 have higher BET specific surface areas.

[0040] The contents of S, C, H, and N elements of the catalysts synthesized at different calcination temperatures in Examples 1-4 are shown in Table 2 below.

[0041] Table 2

[0042] It can be seen from Table 2 that the nitrogen content of the catalyst decreases as the pyrolysis temperature increases, the contents of pyridine nitrogen, graphitic nitrogen, and nitrogen oxide increase as the pyrolysis temperature increases, and pyrrole nitrogen decreases as the pyrolysis temperature increases. Moreover, the S contents of the four catalysts are relatively low, verifying again that the S element will decrease during the pyrolysis process.

[0043] The catalysts prepared in Examples 1-4 were used in the ammoxidation reaction of benzaldehyde. For the specific method, refer to Application Examples 1-4. The results are shown in Table 3 and Figure 8 as follows.

[0044] Table 3

[0045] Application Examples 5-9 The catalyst prepared in Example 4 was used in the ammoxidation reaction of benzaldehyde. 0.5 mmol of benzaldehyde, 3 mL of acetonitrile, 100 mg of CN-900-300, 200 μL of ammonia (ammonia water concentration is 28 wt%), and 0.8 MPa of oxygen (oxygen is 99.99%) were added to a 25 mL reaction kettle for reaction. Under magnetic stirring, the reaction temperature was 60 °C and maintained for 1 or 3 or 4 or 5 h. The specific reaction parameters and results are shown in Table 4 and Figure 9 as follows.

[0046] Table 4

[0047] From Table 4 and Figure 9 it can be seen that in the catalytic ammoxidation reaction of aldehyde by CN-900-300, under certain reaction conditions, as the reaction time increases, the yield of benzonitrile continuously increases and approaches complete reaction at 5 h.

[0048] Application Examples 9-12 The catalyst prepared in Example 4 was used for the ammoxidation reaction of benzaldehyde. 0.5 mmol of benzaldehyde, 3 mL of acetonitrile, 100 mg of CN-900-300, 200 μL of ammonia (ammonia water concentration is 28 wt%), and 0.6 or 0.7 or 0.8 or 1.0 MPa of oxygen (oxygen is 99.99%) were added to a 25 mL reaction kettle for reaction. Under magnetic stirring, the reaction temperature was 60 °C and maintained for 5 h. The specific reaction parameters and results are as shown in Table 5 and Figure 10 as shown below.

[0049] Table 5

[0050] From Table 5 and Figure 10 it can be seen that in the catalytic ammoxidation reaction of aldehyde by CN-900-300, under certain reaction conditions, increasing the oxygen pressure results in a low increase in the yield of benzonitrile. It can be considered that the oxygen pressure is not the main influencing factor in this catalytic system, and a suitable oxygen pressure of 0.8 MPa was screened out. Example 5

[0051] Weigh 4.0027 g of sodium lignosulfonate, 3.0051 g of melamine, and 1.3017 g of potassium hydroxide and mix them using a planetary ball mill (the rotation speed of the planetary ball mill is 400 rpm, and the forward and reverse intermittent ball milling is for 10 h. The forward and reverse intermittent is: pause for 5 min after every 30 min of ball milling), and collect the powder after ball milling;

[0052] Load the above ball-milled powder into an alumina crucible, place the crucible in a tube furnace, introduce nitrogen, and set the heating program: the heating rate is 5 °C / min, the pyrolysis temperature is 900 °C, and the holding time is 60 min for pyrolysis. After pyrolysis, it is cooled naturally. After waiting for the temperature to drop to room temperature, collect the pyrolyzed black powder. The pyrolyzed powder is fully ground using a mortar and then put into a beaker and added with deionized water to a scale of 500 ml, ultrasonically cleaned for 90 min and centrifuged (the rotation speed of the centrifugation is 11,000 rpm, and the centrifugation time is 3 min), filtered. The obtained solid is washed with methanol and centrifuged again, and vacuum dried at 80 °C for 10 h to obtain a metal-free nitrogen-doped lignin-based porous carbon material, and the obtained product is named CN-900-400.

[0053] Application Example 13 The catalyst prepared in Example 5 was used in the ammoxidation reaction of benzaldehyde. 0.5 mmol of benzaldehyde, 3 mL of acetonitrile, 100 mg of CN-900-300, 200 μL of ammonia (ammonia water concentration is 28 wt%), and 1.0 MPa of oxygen (oxygen is 99.99%) were added to a 25 mL reaction kettle for reaction. Under magnetic stirring, the reaction temperature was 60 °C and maintained for 5 h, and the yield of benzonitrile was 97%. Example 6

[0054] Weigh 4.0081 g of sodium lignosulfonate, 3.0079 g of melamine, and 1.3023 g of potassium hydroxide and mix them by a planetary ball mill (the rotation speed of the planetary ball mill is 500 rpm, and the forward and reverse intermittent ball milling is for 10 h. The forward and reverse intermittence is: pause for 5 min after every 30 min of ball milling), and collect the powder after ball milling; Put the above ball-milled powder into an alumina crucible, place the crucible in a tube furnace, and introduce nitrogen. Set the heating program: the heating rate is 5 °C / min, the pyrolysis temperature is 900 °C, and the holding time is 60 min for pyrolysis. After pyrolysis, it is naturally cooled. Wait until the temperature drops to room temperature and then collect the pyrolyzed black powder. The pyrolyzed powder is fully ground using a mortar and then put into a beaker, add deionized water to the scale of 500 ml, perform ultrasonic cleaning for 90 min and centrifuge (the rotation speed of the centrifuge is 11,000 rpm, and the centrifugation time is 3 min) and filter. The obtained solid is washed with methanol and centrifuged again, and vacuum dried at 80 °C for 10 h to obtain a metal-free nitrogen-doped lignin-based porous carbon material, and the obtained product is named CN-900-500.

[0055] Application Example 14 The catalyst prepared in Example 6 was used in the ammoxidation reaction of benzaldehyde. 0.5 mmol of benzaldehyde, 3 mL of acetonitrile, 100 mg of CN-900-300, 200 μL of ammonia (ammonia water concentration is 28 wt%), and 1.0 MPa of oxygen (oxygen is 99.99%) were added to a 25 mL reaction kettle for reaction. Under magnetic stirring, the reaction temperature was 60 °C and maintained for 5 h, and the yield of benzonitrile was 98%. Example 7

[0056] Weigh 4.0033 g of sodium lignosulfonate, 3.0009 g of melamine, and 1.3041 g of potassium hydroxide and mix them by a planetary ball mill (the rotation speed of the planetary ball mill is 600 rpm, and the forward and reverse intermittent ball milling is for 10 h. The forward and reverse intermittence is: pause for 5 min after every 30 min of ball milling), and collect the powder after ball milling; Load the ball-milled powder into an alumina crucible, place the crucible in a tube furnace, introduce nitrogen, and set the heating program: the heating rate is 5 °C / min, the pyrolysis temperature is 900 °C, and the holding time is 60 min. Then carry out pyrolysis and let it cool naturally after pyrolysis. Wait until the temperature drops to room temperature, collect the pyrolyzed black powder. After the pyrolyzed powder is sufficiently ground in a mortar, put it into a beaker, add deionized water to the scale of 500 ml, carry out ultrasonic cleaning for 90 min and centrifuge (the rotation speed of the centrifuge is 11000 rpm and the centrifugation time is 3 min), filter. The obtained solid is washed with methanol and centrifuged again, and then vacuum dried at 80 °C for 10 h to obtain a metal-free nitrogen-doped lignin-based porous carbon material, and the obtained product is named CN-900-600.

[0057] Application Example 14 Use the catalyst prepared in Example 7 for the ammoxidation reaction of benzaldehyde. Add 0.5 mmol of benzaldehyde, 3 mL of acetonitrile, 100 mg of CN-900-300, 200 μL of ammonia (the concentration of ammonia water is 28 wt%), and 1.0 MPa of oxygen (the purity of oxygen is 99.99%) into a 25 mL reaction kettle for reaction. Under magnetic stirring, the reaction temperature is 60 °C and it is maintained for 5 h, and the yield of benzonitrile is 96%.

[0058] The catalysts prepared in Examples 13 - 15 are respectively used for the ammoxidation reaction of benzaldehyde. For the specific method, refer to Application Examples 13 - 15. The specific parameters and results of Application Examples 4, 13 - 15 are as shown in Table 6 and Figure 11 as shown below.

[0059] Table 6

[0060] From Table 6 and Figure 11 it can be seen that changing the rotation speed of the ball mill basically has no great influence on the catalytic reaction of the material. Considering from the perspective of industrial production, a low rotation speed can reduce the energy cost. Therefore, a ball mill rotation speed of 300 rpm is selected as the appropriate preparation condition.

[0061] Application Examples 16 - 19 After the catalyst used in Application Example 4 is recovered, separated, washed, and dried, it is used for the ammoxidation reaction of benzaldehyde. Add 0.5 mmol of benzaldehyde, 3 mL of acetonitrile, 100 mg of CN-900-300 recycled 1 time or 2 times or 3 times or 4 times, 200 μL of ammonia (the concentration of ammonia water is 28 wt%), and 0.8 MPa of oxygen (the purity of oxygen is 99.99%) into a 25 mL reaction kettle for reaction. Under magnetic stirring, the reaction temperature is 60 °C and it is maintained for 5 h. For the specific method, refer to Applications 16 - 19. The specific parameters and results of Application Examples 4, 16 - 19 are as shown in Table 7 and Figure 12 as shown below.

[0062] Table 7

[0063] From Table 7 and Figure 12 it can be seen that the yield of benzonitrile in the four recycling reactions (five uses) of CN-900-300 did not show a significant decrease, indicating that CN-900-300 has good stability and reusability.

[0064] Application Example 19 The catalyst prepared in Example 4 was used for the ammoxidation reaction of benzaldehyde and its derivatives. The reaction conditions were: 0.5 mmol of substrate, 100 mg of catalyst, 0.8 MPa of O2, and 200 μL of ammonia (ammonia water concentration was 28 wt%). The reaction results are shown in Table 8 below.

[0065] Table 8

[0066] From Table 8, it can be seen that in addition to catalyzing the ammoxidation of benzaldehyde to synthesize nitrile compounds, CN-900-300 also has good ammoxidation catalytic ability for other aldehydes under certain reaction conditions, indicating that CN-900-300 has excellent catalytic performance and wide applicability.

[0067] Comparative Example 1 Weighed 4.0102 g of sodium lignosulfonate and 3.0121 g of melamine and added them to a planetary ball mill. Set the rotation speed to 300 rpm and perform intermittent ball milling in both forward and reverse directions for 10 h for mixing (intermittent ball milling in both forward and reverse directions means ball milling for 30 min each time, pausing for 5 min, then changing the rotation direction and continuing to ball mill for 30 min, repeating in turn until the actual ball milling time is 10 h). Collect the powder after ball milling;

[0068] The above ball-milled powder was loaded into an alumina crucible, and the crucible was placed in a tube furnace. Nitrogen was introduced, and the heating program was set as follows: the heating rate was 5 °C / min, the pyrolysis temperature was 900 °C, and the holding time was 60 min for pyrolysis. After pyrolysis, it was cooled naturally; after waiting for the temperature to drop to room temperature, the pyrolyzed black powder was collected. The pyrolyzed powder was thoroughly ground using a mortar and then put into a beaker, and deionized water was added to the scale of 500 ml. It was ultrasonically cleaned for 90 min and then centrifuged and filtered. The obtained solid was washed with methanol and centrifuged again, and vacuum dried at 80 °C for 10 h to obtain a metal-free nitrogen-doped lignin-based porous carbon material, and the obtained product was named CN-900 (without KOH).

[0069] Comparative Application Example 1 The catalyst prepared in Comparative Example 1 was used in the ammoxidation reaction of benzaldehyde. 0.5 mmol of benzaldehyde, 3 mL of acetonitrile, 100 mg of CN-900 (without KOH), 200 μL of ammonia water, and 0.8 MPa of oxygen were added to a 25 mL reaction kettle for reaction. Under magnetic stirring, the reaction temperature was 60 °C and maintained for 5 h, and the yield of benzonitrile was 48%.

[0070] From Comparative Example 1 and Comparative Application Example 1, it can be seen that when the catalyst prepared from the lignin-based carbon material without KOH activation was used in the ammoxidation reaction of benzaldehyde, the yield of benzonitrile was much lower than that when the catalyst prepared from the lignin-based carbon material after activation was used in the ammoxidation reaction of benzaldehyde. This further proves that the catalyst prepared from the KOH-activated lignin-based carbon material has a high BET specific surface area and a porous structure, exposing more active sites and significantly improving the catalytic activity for the oxidative nitrilation of benzaldehyde derivatives to form the corresponding nitriles.

[0071] Comparative Example 2 Weighed 4.0111 g of sodium lignosulfonate and added it to a planetary ball mill. The rotation speed was set at 300 rpm, and it was ball-milled intermittently forward and backward for 10 h for mixing (the intermittent forward and backward ball milling was 30 min of ball milling each time, paused for 5 min, and then the rotation direction was changed to continue ball milling for 30 min, repeating in turn until the actual ball milling time was 10 h). The powder after ball milling was collected;

[0072] The above-mentioned ball-milled powder was loaded into an alumina crucible, and the crucible was placed in a tube furnace. Nitrogen was introduced, and the heating program was set: the heating rate was 5 °C / min, the pyrolysis temperature was 900 °C, and the holding time was 60 min for pyrolysis. After the pyrolysis was completed, it was cooled naturally. After waiting for the temperature to drop to room temperature, the black powder after pyrolysis was collected. The powder after pyrolysis was fully ground in a mortar and then put into a beaker and added with deionized water to a scale of 500 ml, ultrasonically cleaned for 90 min and centrifuged and filtered. The obtained solid was washed with methanol and centrifuged again, and vacuum dried at 80 °C for 10 h to obtain a metal-free nitrogen-doped lignin-based porous carbon material, and the obtained product was named C-900-300.

[0073] Comparative Application Example 2 The catalyst prepared in Comparative Example 2 was used in the ammoxidation reaction of benzaldehyde. 0.5 mmol of benzaldehyde, 3 mL of acetonitrile, 100 mg of C-900-300, 200 μL of ammonia water, and 0.8 MPa of oxygen were added to a 25 mL reaction kettle for reaction. Under magnetic stirring, the reaction temperature was 60 °C and maintained for 5 h, and the yield of benzonitrile was 2%.

[0074] It can be seen from Comparative Example 2 and Comparative Application Example 2 that when the benzaldehyde ammoxidation reaction is catalyzed by the catalyst prepared without melamine raw materials, the yield of benzonitrile is much lower than that when the benzaldehyde ammoxidation reaction is catalyzed by the catalyst prepared from the activated lignin-based carbon material, further proving that the nitrogen functional group plays a key role in the formation of active sites.

[0075] Comparative Example 3 Weigh 3.9938 g of alkali lignin, 2.9885 g of melamine, and 1.2986 g of potassium hydroxide and add them to a planetary ball mill. Set the rotation speed to 300 rpm and perform intermittent ball milling in both forward and reverse directions for 10 h for mixing (intermittent ball milling in both forward and reverse directions means ball milling for 30 min each time, pausing for 5 min, then changing the rotation direction and continuing to ball mill for 30 min, repeating in turn until the actual ball milling time is 10 h), and collect the powder after ball milling.

[0076] Put the powder after ball milling into an alumina crucible, place the crucible in a tube furnace, introduce nitrogen, and set the heating program: the heating rate is 5 °C / min, the pyrolysis temperature is 900 °C, and the holding time is 60 min for pyrolysis. After pyrolysis, let it cool naturally. After waiting for the temperature to drop to room temperature, collect the black powder after pyrolysis. The powder after pyrolysis is fully ground with a mortar and then put into a beaker, add deionized water to the scale of 500 ml, perform ultrasonic cleaning for 90 min and then centrifuge and filter. The obtained solid is washed with methanol and centrifuged again, and vacuum dried at 80 °C for 10 h to obtain a metal-free nitrogen-doped lignin-based porous carbon material, and the obtained product is named CN-900-300 (alkali lignin).

[0077] Comparative Application Example 3 Use the catalyst prepared in Comparative Example 3 for the benzaldehyde ammoxidation reaction. Add 0.5 mmol of benzaldehyde, 3 mL of acetonitrile, 100 mg of CN-900-300 (alkali lignin), 200 μL of ammonia water, and 0.8 MPa of oxygen to a 25 mL reaction kettle for reaction. Under magnetic stirring, the reaction temperature is 60 °C and it is maintained for 5 h, and the yield of benzonitrile is 18%.

[0078] Comparative Example 4 Weigh 4.0123 g of delignified lignin, 3.0126 g of melamine, and 1.3105 g of potassium hydroxide and add them to a planetary ball mill. Set the rotation speed to 300 rpm and perform intermittent ball milling in both forward and reverse directions for 10 h for mixing (intermittent ball milling in both forward and reverse directions means ball milling for 30 min each time, pausing for 5 min, then changing the rotation direction and continuing to ball mill for 30 min, repeating in turn until the actual ball milling time is 10 h), and collect the powder after ball milling.

[0079] Load the ball-milled powder into an alumina crucible, place the crucible in a tube furnace, introduce nitrogen, and set the heating program: the heating rate is 5 °C / min, the pyrolysis temperature is 900 °C, and the holding time is 60 min. Carry out pyrolysis and let it cool naturally after pyrolysis is completed. Wait until the temperature drops to room temperature and then collect the black powder after pyrolysis. The powder after pyrolysis is fully ground in a mortar and then put into a beaker, add deionized water to the scale of 500 ml, carry out ultrasonic cleaning for 90 min and then centrifuge and filter. The obtained solid is washed with methanol and centrifuged again, and vacuum dried at 80 °C for 10 h to obtain a metal-free nitrogen-doped lignin-based porous carbon material. The obtained product is named CN-900-300 (delignified lignin).

[0080] Comparative Application Example 4 Use the catalyst prepared in Comparative Example 4 for the ammoxidation reaction of benzaldehyde. Add 0.5 mmol of benzaldehyde, 3 mL of acetonitrile, 100 mg of CN-900-300 (delignified lignin), 200 μL of ammonia water, and 0.8 MPa of oxygen into a 25 mL reaction kettle for reaction. Under magnetic stirring, the reaction temperature is 60 °C and it is maintained for 5 h. The yield of benzonitrile obtained is 0% (no reaction).

[0081] It can be seen from Comparative Example 3, 4 and Comparative Application Example 3, 4 that when using the catalyst prepared with alkali lignin instead of lignosulfonate for the ammoxidation reaction of benzaldehyde, the yield of benzonitrile is much lower than that of the catalyst prepared with the activated lignin-based carbon material for the ammoxidation reaction of benzaldehyde. This may be because the alkali lignin molecular structure lacks sulfonic acid groups, resulting in uneven distribution of active sites on the carbon skeleton surface and a smaller mesopore volume, which is not conducive to the diffusion and mass transfer of reactant molecules in the pores.

[0082] All in all, the present invention prepares a catalyst by directly pyrolyzing and calcining lignosulfonate, melamine, and potassium hydroxide after ball milling. This preparation method is simple, and the raw material source is environmentally friendly and sustainable. The catalyst prepared by the present invention not only has a metal-free property, but also has high activity, selectivity and applicability. It can catalytically prepare nitriles from aldehydes in one pot with high conversion rate and high selectivity under mild conditions. The formed nitriles will not be further converted into amides and have good tolerance to other oxidizable groups, which proves that the catalyst has great potential.

[0083] The above has described the embodiments of the present invention in detail, but the present invention is not limited to the described embodiments. For those skilled in the art, without departing from the principles and spirit of the present invention, various changes, modifications, substitutions and variations of these embodiments still fall within the protection scope of the present invention.

Claims

1. A preparation method of a non-metal nitrogen-doped lignin-based porous carbon material, characterized in that, It includes the following steps: Mix sodium lignosulfonate, melamine, and potassium hydroxide and ball-mill them. After ball-milling, put the powder into a tubular furnace for pyrolysis at 600 - 900 °C. After pyrolysis, grind the powder, perform ultrasonic cleaning and centrifugation, collect the solid, wash it, and centrifuge it again, then dry it to obtain the non-metal nitrogen-doped lignin-based porous carbon material.

2. The preparation method of the non-metallic nitrogen-doped lignin-based porous carbon material according to claim 1, wherein The mass ratio of sodium lignosulfonate, melamine, and potassium hydroxide is 4:3:1.

3.

3. The preparation method of the non-metallic nitrogen-doped lignin-based porous carbon material according to claim 1, wherein The rotation speed of ball-milling is 300 - 600 rpm, and the ball-milling time is 6 - 10 h.

4. The preparation method of the non-metallic nitrogen-doped lignin-based porous carbon material according to claim 1, characterized in that, The pyrolysis is carried out in a nitrogen atmosphere, with a heating rate of 4 - 6 °C / min to 700 - 900 °C, holding for 60 min, and finally cooling naturally.

5. The preparation method of the non-metallic nitrogen-doped lignin-based porous carbon material according to claim 1, characterized in that The washing is carried out using methanol.

6. A non-metallic nitrogen-doped lignin-based porous carbon material, characterized in that, It is obtained by the preparation method of the non-metal nitrogen-doped lignin-based porous carbon material according to any one of claims 1 - 5.

7. Use of the non-metal nitrogen-doped lignin-based porous carbon material according to claim 6 in the catalytic synthesis of nitriles by aldehyde-ammonia oxidation.

8. A method for synthesizing nitrile by ammoxidation of aldehyde, characterized in that, Add the aldehyde compound and the nitrogen-doped lignin-based porous carbon material according to claim 6 into a reaction kettle, then successively add the solvent and ammonia water, and introduce oxygen to make the final pressure in the reaction kettle 0.6 - 1 MPa, and react at 60 - 80 °C for 1 - 12 h to obtain the nitrile compound.

9. The method for synthesizing nitrile by aldehyde ammoxidation according to claim 8, characterized in that, The aldehyde compound includes at least one of benzaldehyde, 4-methylbenzaldehyde, 4-ethylbenzaldehyde, 4-hydroxybenzaldehyde, 4-fluorobenzaldehyde, 4-chlorobenzaldehyde, 4-bromobenzaldehyde, 4-iodobenzaldehyde, 4-methoxybenzaldehyde, 4-ethoxybenzaldehyde, terephthalaldehyde, 4-biphenylaldehyde, and 2-naphthaldehyde; the solvent is acetonitrile.

10. The method for synthesizing nitrile by aldehyde ammoxidation according to claim 7, wherein, The dosage ratio of the aldehyde compound, the nitrogen-doped lignin-based porous carbon material, and ammonia water is 0.5 mmol: 100 mg: 200 μL; the concentration of the ammonia water is 25 - 30 wt%.

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