阅读说明：本技术 富氮多级孔生物质炭及其应用 (Nitrogen-rich hierarchical pore biomass charcoal and application thereof ) 是由 江霞 袁进 王邦达 张进 蒋文举 于 2019-10-25 设计创作，主要内容包括：本发明公开了一种富氮多级孔生物质炭及其应用,属于环保功能碳材料技术领域。本发明针对目前掺氮生物质炭含氮量低、孔隙结构欠发达等问题,提供了一种新型富氮多级孔生物质炭,其制备方法为：将生物质和氮化碳置于碳酸盐水溶液中,搅拌混合均匀后烘干,烘干后的物料在惰性氛围下加热至800～900℃进行煅烧,煅烧产物经洗涤、干燥,即得产品。本发明采用富氮的氮化碳作为掺氮剂,实现高氮含量掺入,加入活化剂碳酸盐,有效改善了生物质炭的孔隙结构,使生物质炭具有良好的低温脱除硫化氢性能。(The invention discloses nitrogen-rich hierarchical pore biomass charcoal and application thereof, and belongs to the technical field of environment-friendly functional carbon materials. The invention provides novel nitrogen-rich hierarchical pore biomass charcoal aiming at the problems of low nitrogen content, underdeveloped pore structure and the like of the prior nitrogen-doped biomass charcoal, and the preparation method comprises the following steps: placing biomass and carbon nitride in a carbonate water solution, stirring and mixing uniformly, drying, heating the dried material to 800-900 ℃ in an inert atmosphere for calcining, and washing and drying the calcined product to obtain the product. The invention adopts nitrogen-rich carbon nitride as a nitrogen doping agent, realizes high nitrogen content doping, and adds the activating agent carbonate, thereby effectively improving the pore structure of the biomass charcoal and leading the biomass charcoal to have good performance of removing hydrogen sulfide at low temperature.)

1. The nitrogen-rich hierarchical pore biomass charcoal is characterized by being prepared by the following method:

A. placing biomass and carbon nitride in a carbonate aqueous solution, uniformly stirring and drying to obtain a solid mixture;

B. and C, heating the solid mixture obtained in the step A to 800-900 ℃ in an inert atmosphere for calcining, and washing and drying a calcined product to obtain the nitrogen-rich hierarchical pore biomass charcoal.

2. The nitrogen-rich hierarchical pore biomass char of claim 1, characterized in that: in the step A, the carbonate is potassium carbonate or sodium carbonate.

3. The nitrogen-rich hierarchical pore biomass char of claim 2, characterized in that: in the step A, the mass ratio of the biomass to the carbon nitride to the carbonate is 1: 0.01-2: 0.01 to 2; preferably, the mass ratio of the biomass to the carbon nitride to the carbonate is 1: 0.5-2: 0.5 to 2.

4. The nitrogen-rich hierarchical pore biomass char of claim 1, characterized in that: in the step A, the mass ratio of the carbonate water solution to the biomass is 5-10: 1.

5. the nitrogen-rich hierarchical pore biomass char of claim 1, characterized in that: in the step A, the biomass is at least one of cypress chips, poplar chips, coconut shells, peanut shells, walnut shells, straws, sludge, vinasse or corncobs and the like.

6. The nitrogen-rich hierarchical pore biomass char of claim 1, characterized in that: in the step A, the particle size of the biomass is 30-100 meshes; the particle size of the carbon nitride is 30-100 meshes.

7. The nitrogen-rich hierarchical pore biomass char of claim 1, characterized in that: in the step A, mechanical stirring or magnetic stirring is adopted for stirring, and the stirring time is 1-4 h.

8. The nitrogen-rich hierarchical pore biomass char of claim 1, characterized in that: in the step A, the drying temperature is 80-120 ℃, and the drying time is 12-24 hours.

9. The nitrogen-rich hierarchical porous biomass charcoal according to any one of claims 1 to 8, characterized in that: in the step B, the heating rate is 5-20 ℃/min; the calcination time is 1.0-5.0 h.

10. Use of the nitrogen-enriched hierarchical porous biomass charcoal according to any one of claims 1 to 9 for removing hydrogen sulfide.

Technical Field

The invention belongs to the technical field of carbon materials with environmental protection functions, and particularly relates to nitrogen-rich hierarchical porous biomass carbon and application thereof.

Background

The nitrogen-doped carbon material has wide application prospects in the fields of adsorption, catalysis, gas separation and storage, energy storage and conversion and the like. The nitrogen atom doping can effectively improve the physicochemical property of the porous carbon. The extra lone pair of electrons of the nitrogen atom can endow negative charges of a delocalized pi system in an sp2 hybridized carbon skeleton, so that the electron transfer performance and the chemical reaction activity of the carbon material are enhanced; meanwhile, charge delocalization caused by nitrogen atom doping can change O₂Adsorption on carbon material by means of O₂The adsorption mode of molecules is changed from point adsorption to side adsorption, which is more favorable for O₂The molecules are reduced to produce more active oxygen. In addition, nitrogen atoms doped in the carbon material can enhance the surface alkalinity of the carbon material, strengthen the interaction of dipole-dipole bonds, hydrogen bonds and covalent bonds between the surface of the carbon material and acidic substance molecules, and improve the selective effect of the carbon material on the acidic substance.

Nitrogen-doped carbon materials are generally prepared by in-situ nitrogen doping and post-treatment nitrogen doping. The post-treatment nitrogen doping is to carry out post-treatment on the synthesized carbon material by adopting a nitrogen-containing chemical reagent, and the method not only needs to be carried out step by step, but also has low nitrogen content in the prepared carbon material. In-situ nitrogen doping is to directly dope nitrogen atoms in the process of synthesizing the carbon material, and mainly comprises a template method, chemical vapor deposition, hydrothermal method and the like. The nitrogen-doped carbon material prepared by the method has high nitrogen content, but the pore structure is single, the raw material mainly adopts a nitrogen-containing chemical reagent, strong corrosive materials such as acid and alkali and a template agent are needed in the preparation process, the operation is complex, the production cost is high, the generated pollution is also large, and therefore the application of the nitrogen-doped carbon material is also greatly limited.

The method for preparing the nitrogen-doped porous carbon by using the biomass as the raw material in one step is a new technology developed in recent years, can utilize the biomass widely existing in the nature as resources, and has the advantages of simple process and convenient operation. At present, ammonium salts such as ammonium nitrate, ammonium oxalate, ammonium chloride and the like and nitrogen-containing organic matters such as urea, amide, melamine and the like are mainly used as nitrogen doping agents for preparing nitrogen-doped biomass charcoal. However, because the decomposition temperature of the ammonium salt and the nitrogenous organic matter is lower (less than or equal to 350 ℃) and the carbonization temperature of the biomass is higher (more than or equal to 500 ℃), in the calcining process, the nitrogen-doped agent can decompose and release nitrogenous gas before the biomass is carbonized, so that the nitrogenous gas and a carbon matrix formed by carbonization cannot fully react, the nitrogen content of the biomass carbon prepared by the method is lower, and the doped nitrogen content is not more than 8.0 wt%. In addition, the biomass charcoal prepared by the method has a poor pore structure.

201610492985.3 discloses a nitrogen-doped hierarchical porous carbon and its preparation method and application, wherein the nitrogen-doped hierarchical porous carbon is prepared by using biomass as raw material, using sodium bicarbonate and ammonium oxalate as composite activating agent, and carrying out the treatment processes of calcining, washing, drying, etc., the nitrogen content of the nitrogen-doped biological carbon prepared by the method is only 2.1 wt%, and the specific surface area is only 914m at most²(ii) in terms of/g. For another example, 201510576495.7 discloses a convenient preparation method of biomass-based nitrogen-doped activated carbon, which is characterized in that bean dregs are used as raw materials, potassium carbonate and ammonium bicarbonate are used as modifiers, and the nitrogen-doped activated carbon is prepared by grinding, dry mixing and high-temperature calcination. The biochar prepared by the patent document has the nitrogen content of 1.0-8.0 wt%, the doped nitrogen content is not high, the pore structure is underdeveloped, and the specific surface area is 830-1180m²/g。

The nitrogen content of the currently prepared nitrogen-doped biomass charcoal is low, the pore structure is underdeveloped, the performance of the biomass charcoal is improved to a limited extent, and the application of the nitrogen-doped biomass charcoal is greatly limited.

Disclosure of Invention

Aiming at the problems of low nitrogen content, underdeveloped pore structure and the like existing in the prior method for preparing nitrogen-doped carbon by adopting biomass as a raw material, the invention provides a one-step method for preparing nitrogen-doped biomass carbon, which is simple to operate and low in cost, and biomass is converted into biomass carbon with high nitrogen content and rich hierarchical pore channels.

A novel nitrogen-rich hierarchical pore biomass charcoal is prepared by the following method:

A. placing biomass and carbon nitride in a carbonate aqueous solution, stirring, and drying to obtain a mixture;

B. and C, heating the mixture obtained in the step A to 800-900 ℃ in an inert atmosphere for calcining, and washing and drying a calcined product to obtain the nitrogen-rich hierarchical pore biomass charcoal.

Wherein, in the step A, the carbonate is potassium carbonate or sodium carbonate.

In the step A, the mass ratio of the biomass to the carbon nitride to the carbonate is 1: 0.01-2: 0.01 to 2.

Preferably, in the nitrogen-enriched hierarchical porous biomass charcoal, in the step a, the mass ratio of the biomass to the carbon nitride to the carbonate is 1: 0.5-2: 0.5 to 2.

In the step A, the mass ratio of the carbonate aqueous solution to the biomass is 5-10: 1.

in the step A, the biomass is at least one of cedar wood chips, poplar wood chips, coconut shells, peanut shells, walnut shells, straws, sludge, vinasse or corncobs.

In the step A, the particle size of the biomass is 30-100 meshes.

In the step A, the particle size of the nitrogen-rich hierarchical porous biomass charcoal is 30-100 meshes.

And B, stirring the nitrogen-enriched hierarchical porous biomass carbon in the step A by adopting mechanical stirring or magnetic stirring for 1-4 h.

In the step A, the drying temperature is 80-120 ℃, and the drying time is 12-24 hours.

Wherein in the step B, the heating rate of the nitrogen-rich hierarchical porous biomass carbon is 5-20 ℃/min; the calcination time is 1.0-5.0 h.

The nitrogen-rich hierarchical porous biomass carbon provided by the invention has the advantages of high nitrogen content, large specific surface area, developed micropore and mesopore structure, excellent desulfurization performance and capability of being used for efficiently removing hydrogen sulfide.

Has the advantages that:

the invention adopts nitrogen-rich carbon nitride as a nitrogen doping agent, which releases NH in the decomposition process at 550-779 DEG C₃Released NH₃The nitrogen-containing functional group can react with a carbon matrix formed after biomass carbonization, so that the nitrogen-containing functional group is introduced into a biomass carbon skeleton structure, the problem that a common nitrogen source decomposes and releases nitrogen-containing gas before raw material carbonization to cause ineffective reaction with the carbon matrix is solved, and high nitrogen doping amount is realized; meanwhile, the activating agent carbonate is added, so that the pore structure of the biomass charcoal is effectively adjusted, and the biomass charcoal has rich micropores and mesopore structures; the invention adopts a one-step method to prepare the nitrogen-doped biomass carbon, the nitrogen doping and the activation processes are carried out simultaneously, the nitrogen content of the obtained nitrogen-rich hierarchical porous biomass carbon is up to 14.2 wt%, and the specific surface area is up to 2459m²(g) total pore volume of 1.453m³The mesopore volume can reach 0.597m³Per g, micropore volume up to 0.474m³Has excellent desulfurization performance.

Drawings

Fig. 1 is a thermogravimetric plot of wood chips in example 1.

FIG. 2 is a graph showing the thermogravimetric curves of carbon nitride in example 1.

FIG. 3 is a graph showing the gaseous products released during pyrolysis of carbon nitride in example 1.

FIG. 4 is a nitrogen adsorption isotherm of the biomass char in example 1.

FIG. 5 is an X-ray photoelectron spectrum of the biomass char in example 1.

FIG. 6 is a breakthrough curve for the removal of hydrogen sulfide from biomass char in example 2.

Detailed Description

Specifically, the nitrogen-rich hierarchical pore biomass charcoal is prepared by the following method:

A. placing biomass and carbon nitride in a carbonate aqueous solution, uniformly stirring and drying to obtain a solid mixture;

B. and C, heating the solid mixture obtained in the step A to 800-900 ℃ in an inert atmosphere for calcining, and washing and drying a calcined product to obtain the nitrogen-rich hierarchical pore biomass charcoal.

The inventor firstly researches the pyrolysis characteristics of biomass and carbon nitride, and finds that the decomposition temperature of the carbon nitride is equivalent to the carbonization temperature of the biomass, so that nitrogen-rich Carbon Nitride (CN) is adopted as a nitrogen doping agent, and the nitrogen-containing functional groups can be more favorably introduced into the biomass carbon.

The biomass of the invention has wide sources, such as cypress sawdust, poplar sawdust, coconut shells, peanut shells, walnut shells, straws, sludge, vinasse or corn cobs and the like.

The invention adopts potassium carbonate or sodium carbonate as an activating agent to improve the pore structure of the biomass charcoal. In the step A, potassium carbonate or sodium carbonate is prepared into an aqueous solution, biomass and carbon nitride are mixed in the aqueous solution of carbonate, and the biomass and the carbon nitride are uniformly impregnated by stirring to form a uniform mixture, so that nitrogen elements doped in a prepared sample are uniformly distributed and a pore structure is uniformly formed, and severe etching does not occur.

Research on the influence of carbon nitride and potassium carbonate on the performance of the biomass carbon shows that the low addition of carbon nitride can result in the low nitrogen content in the biomass carbon, the low addition of potassium carbonate can result in poor pore structure, the high addition of carbon nitride and potassium carbonate can result in the high content of macropores in the pore structure, and the macropores have no obvious adsorption effect on sulfur dioxide, hydrogen sulfide and other small molecular gases. Therefore, in the step A of the invention, the mass ratio of the biomass to the carbon nitride to the potassium carbonate is controlled to be 1: 0.01-2: 0.01-2, so that a large number of nitrogen-containing functional groups are introduced into the biomass carbon, and the biomass carbon has a developed micropore and mesopore structure; preferably, the mass ratio of the biomass to the carbon nitride to the potassium carbonate is 1: 0.5-2: 0.5 to 2.

In order to uniformly impregnate the biomass and the carbon nitride and facilitate subsequent drying, the mass ratio of the carbonate aqueous solution to the biomass is 5-10: 1.

in the step A, mechanical stirring or magnetic stirring can be adopted, and stirring is carried out for 1-3 hours, so that the biomass and the carbon nitride are fully and uniformly impregnated; and drying the stirred materials at the temperature of 80-120 ℃ for 12-24 h.

In order to facilitate the pyrolysis, carbonization and decomposition of the carbon nitride of the biomass, it is ensured that the carbon nitride accounts for the ammonia (NH) evolved₃) The biomass carbonization reaction kettle can fully react with a carbon substrate carbonized by sawdust, the particle size of biomass is controlled to be 30-100 meshes, and the particle size of carbon nitride is controlled to be 30-100 meshes.

Tests show that the temperature range of the pyrolysis stage of the biomass is 206-500 ℃, and wood dust rapidly loses weight in the temperature range; when the temperature is higher than 500 ℃, the wood chips enter a carbonization stage, the quality loss is reduced, and a stable carbon structure is formed at about 800 ℃; at a temperature lower than 500 ℃, the mass of the carbon nitride is basically kept unchanged, and when the temperature is higher than 550 ℃, the carbon nitride starts to decompose and rapidly loses weight to generate volatile gas NH₃The decomposition is completed at 779 ℃. Thus, the carbon nitride decomposes to release NH₃Is higher than the pyrolysis temperature of the biomass, is equivalent to the carbonization temperature thereof, which is favorable for NH₃Reacts with the carbon matrix formed by biomass pyrolysis, and avoids the problem that the nitrogen-containing gas is separated out and the carbon matrix can not fully react due to the decomposition of the nitrogen source before the carbonization of the raw material. Based on the rule, in the step B, the biomass charcoal is calcined at the temperature rise rate of 5-20 ℃/min to 800-900 ℃, so that a large amount of nitrogen is doped into the biomass charcoal; in order to ensure complete carbonization of biomass and decomposition of carbon nitride, the calcination time is generally 1-5 h.

The present invention is further illustrated by the following examples, which are not intended to limit the scope of the invention.