阅读说明：本技术 一种棒状六方氮化硼泡沫的制备方法及其丙烷氧化脱氢应用 (Preparation method of rod-shaped hexagonal boron nitride foam and application of rod-shaped hexagonal boron nitride foam in oxidative dehydrogenation of propane ) 是由 黄彩进 刘秋文 于 2019-10-18 设计创作，主要内容包括：本发明公开了一种棒状六方氮化硼泡沫的制备方法及其丙烷氧化脱氢应用,涉及材料科学技术和石油化工领域。本发明提出了一种棒状六方氮化硼泡沫的制备方法,利用了三聚氰胺和硼酸水解聚合反应。干燥的前驱体在氨气中退后之后,生成的六方氮化硼为白色泡沫状固体。这个泡沫由孔孔(约100 nm尺寸)相连的棒状六方氮化硼架构而成。这种孔结构有利于气体的流通和扩散,具有很好的作为多相催化剂的潜力。棒状六方氮化硼泡沫表现了优异的丙烷脱氢性能。本发明方法简单,产率高,有利于大规模的工业生产,具备显著的经济和社会效益。(The invention discloses a preparation method of rod-shaped hexagonal boron nitride foam and application of the rod-shaped hexagonal boron nitride foam in propane oxidative dehydrogenation, and relates to the fields of material science and technology and petrochemical industry. The invention provides a preparation method of bar-shaped hexagonal boron nitride foam, which utilizes the hydrolytic polymerization reaction of melamine and boric acid. After the dried precursor was withdrawn in ammonia gas, the hexagonal boron nitride produced was a white foamy solid. This foam is constructed of hexagonal boron nitride rods with connected pores (about 100 nm in size). The pore structure is beneficial to the circulation and diffusion of gas and has good potential as a heterogeneous catalyst. The rod-shaped hexagonal boron nitride foam shows excellent propane dehydrogenation performance. The method is simple, has high yield, is beneficial to large-scale industrial production, and has remarkable economic and social benefits.)

1. A preparation method of bar-shaped hexagonal boron nitride foam is characterized by comprising the following steps: boric acid and melamine are used as raw materials, and porous rod-shaped hexagonal boron nitride foam is generated in a high-temperature annealing process by utilizing polymerized boric acid and melamine precursors.

2. The method of claim 1, wherein the hexagonal boron nitride rod foam is prepared by: the method specifically comprises the following steps:

(1) dissolving melamine in 100 mL of boiling water containing boric acid to form a colorless transparent state, cooling to room temperature, and condensing an aqueous solution into white hydrogel;

(2) vacuum until the white hydrogel is freeze-dried, and a white foam precursor is obtained;

(3) and placing the mixture in a tubular furnace for high-temperature annealing and naturally cooling to obtain a white foam sample.

3. The method of claim 2, wherein the hexagonal boron nitride rod foam is prepared by: the molar ratio of melamine to boric acid is 1: 2.

4. The method of claim 2, wherein the hexagonal boron nitride rod foam is prepared by: the vacuum freeze-drying conditions are as follows: -20 ℃.

5. The method of claim 2, wherein the hexagonal boron nitride rod foam is prepared by:

the high-temperature annealing is carried out under the condition of ammonia atmosphere.

6. The method of claim 2, wherein the hexagonal boron nitride rod foam is prepared by:

the specific conditions of the high-temperature annealing are as follows: controlling the temperature by program, heating up at a rate of 5 ℃/min, and annealing at 800 ℃ for 5 h.

7. Use of hexagonal boron nitride foam in stick form obtained by the process according to any one of claims 1 ~ 6 in the catalytic dehydrogenation of propane to propylene.

Technical Field

The invention discloses a preparation method of rod-shaped hexagonal boron nitride foam and application of the rod-shaped hexagonal boron nitride foam in propane oxidative dehydrogenation, and relates to the fields of material science and technology and petrochemical industry.

Background

The morphology and structure of a material has a significant impact on its properties and applications. The foam material has the properties of low density, large specific surface area, porosity, higher loading capacity and the like, and has wide application in the fields of heat insulation, gas sensing, energy and catalysis. Recently, hexagonal boron nitride has been found to have excellent oxidative dehydrogenation properties for short-chain alkanes. However, when it is used as an oxidative dehydrogenation catalyst, it is often in a powder state, and a large pressure drop is easily caused in a plug flow type reactor, and the external diffusion of a reaction substrate and a product is affected, so that there is a phenomenon that the catalytic reaction is difficult to control. Therefore, granulation is conventionally required before the reaction to reduce the gas resistance, which increases the flow of preparation of the catalyst, affecting the efficiency. Therefore, the development of the hexagonal boron nitride material with low air resistance and easy reaction control as the alkane oxidative dehydrogenation catalyst has important significance.

Disclosure of Invention

The invention aims to provide a simple, high-efficiency and low-cost method for preparing a hexagonal boron nitride foam material, and the hexagonal boron nitride foam material is used for propane oxidative dehydrogenation. According to the invention, boric acid and melamine are used as raw materials to prepare a hydrogel precursor, and the foam precursor is subjected to vacuum freeze-drying before high-risk roasting, so that the rod-shaped hexagonal boron nitride foam material is finally obtained. The material is used for the reaction of preparing propylene by oxidative dehydrogenation of propane, and shows excellent catalytic performance. The method is simple and convenient to operate, low in cost, has a large-scale commercial production prospect, and has reference significance for preparation and application of other foam materials.

In order to achieve the purpose, the invention adopts the following technical scheme:

a preparation method of rod-shaped hexagonal boron nitride foam specifically comprises the following steps:

the method specifically comprises the following steps:

(1) dissolving melamine in 100 mL of boiling water containing boric acid to form a colorless transparent state, cooling to room temperature, and condensing an aqueous solution into white hydrogel;

(2) vacuum until the white hydrogel is freeze-dried, and a white foam precursor is obtained;

(3) and placing the mixture in a tubular furnace for high-temperature annealing and naturally cooling to obtain a white foam sample.

Further, the molar ratio of melamine to boric acid is 1: 2.

Further, the vacuum freeze-drying conditions are as follows: -20 ℃.

Further, the high-temperature annealing is performed under the condition of an ammonia atmosphere.

Further, the specific conditions of the high-temperature annealing are as follows: controlling the temperature by program, heating up at a rate of 5 ℃/min, and annealing at 800 ℃ for 5 h.

The rod-shaped hexagonal boron nitride foam obtained by the preparation method is used for catalyzing propane dehydrogenation to prepare propylene as a reaction catalyst.

The invention has the beneficial effects that:

(1) a method for preparing a rod-shaped hexagonal boron nitride foam material was developed.

(2) The excellent performance of preparing propylene by oxidative dehydrogenation of propane is obtained.

(3) Has reference significance for expanding the hexagonal boron nitride foam material.

Drawings

FIG. 1 is a schematic diagram of a process for preparing hexagonal boron nitride in rod form.

FIG. 2 is an X-ray powder diffraction (XRD) pattern of hexagonal boron nitride foam in stick form prepared in example 1.

FIG. 3 is an X-ray photoelectron spectroscopy (XPS) of hexagonal boron nitride foam rod prepared in example 1.

FIG. 4 is a Scanning Electron Microscope (SEM) image of a rod-shaped hexagonal boron nitride foam prepared in example 1.

In FIG. 5, a and B are TEM images, c is HRTEM image, d is HADDF image, and e and f are element distribution diagrams of B and N corresponding to d image positions of boron phosphate hollow sphere foam material prepared in example 1.

In fig. 6, a is a graph of the conversion rate and selectivity of the bar-shaped hexagonal boron nitride foam prepared in example 1 for catalyzing propane dehydrogenation to prepare propylene, and b is a graph comparing the performance of the bar-shaped hexagonal boron nitride foam with that of commercial flake hexagonal boron nitride.

Detailed Description

In order to make the present invention more comprehensible, the technical solutions of the present invention are further described below with reference to specific embodiments, but the present invention is not limited thereto.

The preparation method comprises the following steps:

adding a certain amount of melamine into a boiling water solution of boric acid, dissolving the melamine to be transparent, and naturally cooling the melamine to room temperature to obtain hydrogel. The hydrogel was freeze dried in vacuo and placed in an alumina crucible. Under an ammonia atmosphere, with 5^oC/min heating to 800^oAnd C, preserving the heat for 5 hours, and then naturally cooling to obtain a white foam sample, namely the rod-shaped hexagonal boron nitride foam material.