CN114890405A

CN114890405A - Method for low-temperature rapid hydrothermal synthesis of submicron carbon spheres from cellulose

Info

Publication number: CN114890405A
Application number: CN202210694465.6A
Authority: CN
Inventors: 周会; 于士杰; 李清海; 张衍国; 杨潇潇
Original assignee: Tsinghua University
Current assignee: Tsinghua University
Priority date: 2022-06-16
Filing date: 2022-06-16
Publication date: 2022-08-12

Abstract

The invention discloses a method for low-temperature rapid hydrothermal synthesis of submicron carbon spheres by cellulose, which comprises the steps of placing cellulose and water into a reaction kettle according to the mass ratio of (1-3):50, and raising the pressure of the reaction kettle and maintaining the pressure at the reaction pressure of 8-20 MPa; heating the reaction kettle to a preset temperature, maintaining the temperature for 0-30min after the preset temperature is reached, stopping heating, and cooling the reaction kettle, wherein the preset temperature is 200-250 ℃; and filtering the cooled reaction product in the reaction kettle to obtain a solid product, and drying to obtain the submicron carbon spheres. The invention has the advantages of mild condition, quick reaction, simple method and the like.

Description

Method for low-temperature rapid hydrothermal synthesis of submicron carbon spheres from cellulose

Technical Field

The invention relates to a method for synthesizing submicron carbon spheres, in particular to a method for synthesizing carbon spheres by cellulose through low-temperature rapid hydrothermal synthesis, and belongs to the technical field of carbon material synthesis.

Background

The consumption of fossil fuels produces more and more carbon dioxide, which can have serious consequences such as climate change and ocean acidification. Biomass, such as wood, grass and agricultural wastes (straw), is composed of cellulose, hemicellulose and lignin, a renewable, carbon-neutral resource. The utilization of biomass has great potential in reducing global net carbon emissions. Traditional uses of biomass, such as combustion, gasification and anaerobic digestion, are carbon neutral. The biomass is converted into the carbon material, so that the stable carbon storage in a solid form can be realized, and the method is a carbon negative emission technology.

Carbon materials play a crucial role in many energy and environment-related applications, however, the synthesis of carbon materials is generally highly dependent on traditional fossil energy sources, such as by steam reforming or chemical vapor deposition. If biomass can be used as a carbon source in the carbon material synthesis process instead of fossil energy, great contribution can be made to carbon emission reduction. The hydrothermal process of biomass can produce solid carbon materials, which have certain applications in the fields of supercapacitors, wastewater treatment, fuel cells, and the like.

Cellulose is the highest content of a component in biomass, the content of the cellulose in the biomass is up to 40-50%, and the cellulose is also the widest-distributed and highest-content renewable component in nature. Conventional hydrothermal reactions of cellulose tend to be carried out under autogenous pressure, i.e., saturated vapor pressure of water, which is 1.6MPa at 200 ℃. Thus, conventional hydrothermal reactions of cellulose tend to require higher temperatures (>210 ℃) and longer isothermal times (>2h) to promote their decomposition.

Disclosure of Invention

The invention aims to provide a method for low-temperature rapid hydrothermal synthesis of submicron carbon spheres by cellulose, which overcomes the limitations of high temperature and long constant temperature time of the traditional reaction and realizes the low-temperature hydrothermal synthesis of the submicron carbon spheres by utilizing the improvement of the pressure of a reaction system.

The invention is realized by the following technical scheme:

a method for low-temperature rapid hydrothermal synthesis of submicron carbon spheres by cellulose comprises the following steps:

placing cellulose and water into a reaction kettle according to the mass ratio of (1-3) to 50, and increasing the pressure of the reaction kettle and maintaining the pressure at a preset reaction pressure, wherein the preset reaction pressure is 8-20 MPa; heating the reaction kettle to a preset temperature, and stopping heating when the preset temperature is reached, wherein the preset temperature is 200-250 ℃;

and cooling the reaction kettle, filtering the reaction product in the reaction kettle to obtain a solid product, and drying to obtain the submicron carbon spheres.

In the technical scheme, after the expected temperature is reached and the reaction pressure is kept for 0-30min, the heating is stopped.

In the technical scheme, the pressure of the reaction kettle can be increased and maintained by introducing inert gas into the reaction kettle or communicating a high-pressure pump.

In the technical scheme, the average particle size of the cellulose is less than or equal to 1 mm.

In the technical scheme, the reaction kettle is heated by adopting programmed heating, and the heating rate is 1-10 ℃/min.

Compared with the prior art, the invention has the following advantages and prominent effects:

the invention selects cellulose, and can effectively improve the energy of water molecules and promote the catalytic action of water in the reaction process by coupling proper reaction temperature and higher reaction pressure, thereby reducing the reaction time in the hydrothermal carbon material synthesis process. The preparation method of the submicron carbon spheres has the advantages of mild conditions, quick reaction and simple method.

Drawings

Fig. 1 is a scanning electron micrograph of the submicron carbon sphere prepared in example 1.

Fig. 2 is a scanning electron micrograph of the submicron carbon spheres prepared in example 2.

Fig. 3 is a scanning electron micrograph of the submicron carbon spheres prepared in example 3.

Detailed Description

The following will further describe the specific implementation and operation of the present invention with reference to the drawings and examples.

Placing cellulose and water into a reaction kettle according to the mass ratio of (1-3) to 50. Microcrystalline cellulose is generally selected, the cellulose having an average particle size of 1mm or less. The reaction kettle is a high-pressure reaction kettle or a sleeve type reaction kettle, and is provided with a heating device, a pressure stabilizing device and the like. The pressure of the reaction kettle can be increased and maintained by introducing inert gas into the reaction kettle or communicating a high-pressure pump, wherein the inert gas comprises nitrogen and argon. As will be understood and appreciated by those of ordinary skill in the art, will not be described in detail herein.

After the reaction kettle containing the cellulose and the water is sealed, the pressure stabilizing device is started to increase the pressure of the reaction kettle and maintain the pressure at the reaction pressure. The reaction pressure is 8-20 MPa. Heating the reactor to raise the temperature of the reaction kettle to a preset temperature, wherein as one implementation mode, the reaction kettle is heated by adopting programmed temperature raising, and the temperature raising rate is 1-10 ℃/min. Maintaining for 0-30min when the desired temperature is reached, and stopping heating. The preset temperature is 200-250 ℃. The temperature is maintained for 0min, namely the heating is stopped immediately after the expected temperature is reached.

The reaction kettle was allowed to cool. The cooling mode is natural cooling or natural cooling and ice water bath cooling. In the latter embodiment, the temperature of the reaction kettle is first reduced to below 100 ℃ by natural cooling, and then the reaction kettle is immersed in an ice water bath for cooling, and at this time, a sleeve type reaction kettle is usually selected and includes a tubular reaction kettle and a jacket type heating device. As one embodiment, the reaction kettle is heated by adopting temperature programming, and the temperature rise rate is 1-10 ℃/min.

And filtering the cooled reaction product in the reaction kettle to obtain a solid product, and drying to obtain the submicron carbon spheres. The filtration mode comprises centrifugal filtration, suction filtration and the like.

The following examples will further illustrate the performance of the process of the present invention.

Example 1

2g of microcrystalline cellulose was taken into a 50ml hydrothermal reactor, the reactor was sealed, the reactor pressure was raised to 20MPa (i.e. the preset reaction pressure was 20MPa), and heating of the reactor was started. When the temperature of the reactor is raised to 200 ℃ (namely the expected reaction temperature is 200 ℃), stopping heating (namely the reactor is not subjected to heat preservation for any time), directly cooling the reactor to room temperature (cooling by using an ice water bath at the temperature of below 100 ℃), filtering and drying to obtain the submicron carbon spheres with the yield of 44%. The constant temperature time of the whole process is 0, which is far lower than that of the traditional method. At this time, the total of the temperature increase time and the temperature decrease time was about 1.5 hours. FIG. 1 shows that the carbon material prepared by the low-temperature hydrothermal method in example 1 has good submicron sphere morphology, and the average diameter of submicron carbon spheres is 383 nm.

Example 2

The reaction conditions were the same as in example 1 except that the predetermined reaction pressure in example 1 was set to 8 MPa. FIG. 2 shows that the carbon material prepared by low temperature hydrothermal method in example 2 has good submicron sphere morphology, and the average diameter of the submicron carbon spheres is 251 nm. The submicron carbon sphere solids yield was 39% at this time.

Example 3

The desired reaction temperature as described in example 1 was set to 250 ℃ and the other reaction conditions were the same as in example 1. Under these conditions, the total of the temperature increase time and the temperature decrease time was about 2 hours. The carbon material prepared by the low-temperature hydrothermal method in the figure 3 has good submicron sphere morphology, and the average diameter of the submicron carbon spheres is 324 nm. The submicron carbon sphere solids yield was 38% at this time.

Examples 4 and 5 were conducted by changing the mass ratio of cellulose to water in example 1 to 1:50 and 3:50, respectively. Other reaction conditions were the same as in example 1, and submicron carbon spheres were obtained.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. The method for low-temperature rapid hydrothermal synthesis of the submicron carbon spheres by the cellulose is characterized by comprising the following steps:

placing cellulose and water into a reaction kettle according to the mass ratio of (1-3) to (50), and increasing the pressure of the reaction kettle and maintaining the pressure at a preset reaction pressure, wherein the preset reaction pressure is 8-20 MPa; heating the reaction kettle to a preset temperature, and stopping heating when the preset temperature is reached, wherein the preset temperature is 200-250 ℃;

2. The method of claim 1, wherein the heating is stopped after the desired temperature is reached and maintained at the desired temperature and the predetermined reaction pressure for 0-30 min.

3. The method according to claim 1, wherein the cellulose has an average particle size of 1mm or less.

4. The method of claim 1, wherein the reaction kettle is heated at a temperature programmed to 1-10 ℃/min.