Method for preparing porous carbon material from aldose-saccharide compound, porous carbon material and application

Abstract

The invention discloses a method for preparing a porous carbon material from an aldose-saccharide compound, the porous carbon material and application of the porous carbon material. The preparation method comprises the following steps: directly carrying out pyrolysis on a certain mass of aldose-saccharide compound at a certain heating rate to reach a specified temperature in the atmosphere of inert gases such as nitrogen or argon, and then naturally cooling to obtain the uniform porous carbon material. The porous carbon material can be used as an adsorption separation material for methane and nitrogen, and is used for separating methane and nitrogen. Compared with the limitation that an activating agent is added into a traditional organic precursor for pyrolysis to obtain porous carbon and the pore diameter of the porous carbon is difficult to regulate and control, the prepared porous carbon can be directly pyrolyzed without adding the activating agent, the pore diameter and the pore volume can be accurately controlled by controlling the pyrolysis temperature and the heating rate, the process is simple, and the method is suitable for industrial production. The method is reliable and low in cost.

Description

Technical Field

[0001] The present invention belongs to the field of new material industry, and particularly relates to a method for preparing porous carbon materials from aldose compounds and the application of the prepared porous carbon materials as adsorption and separation materials in the field of unconventional natural gas separation and purification. Background Art

[0002] Natural gas (mainly composed of methane, CH 4 ) is a relatively clean primary low-carbon energy source because it only produces carbon dioxide and water after combustion, and has been vigorously developed and applied in recent years. Coalbed methane, as a by-product during coal mining, mainly consists of methane. In actual mining, it will be mixed with air (nitrogen), resulting in concentration fluctuations. High-concentration methane can be directly incorporated into the natural gas pipeline network for use, while low-concentration methane generally cannot be directly utilized and is discharged, increasing the greenhouse effect due to its low calorific value. Therefore, separating and concentrating methane from methane-nitrogen mixtures is of great significance for the effective supplement of natural gas and the reduction of greenhouse gas emissions.

[0003] As the most commonly used porous adsorbent, porous carbon materials have the characteristics of high specific surface area, strong stability, and can be industrially produced, and are widely used in adsorption and separation fields such as water treatment, gas adsorption, and air purification. Among the preparation methods of porous carbon, the most common is to use an organic precursor and an activator, which are mixed by impregnation or grinding, and then subjected to high-temperature activation in a tube furnace under an inert atmosphere, relying on the chemical reaction between the activator and carbon at high temperature to create pore sizes. For example, in Chinese Patent CN118183733A, the carbon precursor is pre-carbonized first, then mixed with an activator and subjected to high-temperature activation, and finally pickled to obtain porous carbon materials. The preparation process of its porous carbon is not only cumbersome, but also has high energy consumption and the generation of waste acid and metal waste liquid. There are also some porous carbon materials that use sacrificial templating agents as the preparation method of microporous carbon, which not only greatly increases the use cost of porous carbon, but also has many limitations for the materials used as templating agents. Although some do not require an activator, they require multi-step treatment schemes, such as pre-hydrothermal reaction or chemical modification using strong acids and bases. Summary of the Invention

[0004] In view of the above traditional porous carbon preparation methods, the present invention uses aldose compounds as carbon precursors and cleverly utilizes the chemical structure characteristics of these compounds to propose a method for preparing porous carbon materials from aldose compounds by a one-step method. The method for directly preparing porous carbon with a carbon precursor having the structural characteristics of aldose proposed by the present invention has the characteristics of simple process and easy preparation, providing a new idea for the synthesis of porous carbon materials and the screening of carbon precursors.

[0005] The present invention is realized through the following technical solutions:

[0006] A method for preparing porous carbon materials from aldose compounds uses aldose compounds as carbon precursors, heats them at a heating rate of 2-10 °C / min to 800-900 °C in an inert atmosphere, holds the temperature for 0.5-3 h, and then cools to room temperature to obtain the porous carbon materials.

[0007] Preferably, the aldose compounds are oxygen-containing heterocyclic compounds containing acetal or hemiacetal structures.

[0008] More preferably, the oxygen-containing heterocyclic compounds are any one of glucose, sucrose, fructose, L-arabinose, D-ribose, cyclodextrin, starch, cellulose, propanalose, butanalose, pentanalose, hexanalose, furfural, cyclohexanone, cyclic ether, furan and furan derivatives, pyran and pyran derivatives.

[0009] Further preferably, the furan derivatives are any one of methyl-β-D-ribofuranoside and β-D-fructofuranose.

[0010] In the above method, the inert atmosphere is any one of nitrogen atmosphere, argon atmosphere or helium atmosphere; the programmed heating rate is preferably 5 °C / min, heated to 900 °C, and the holding time is 2 h.

[0011] The porous carbon material prepared by the above method is characterized in that the porous carbon material has a uniform micropore distribution, and the pore size distribution is concentrated in the range of 0.5nm-0.8nm.

[0012] The porous carbon material prepared by the above method has an equilibrium adsorption capacity for methane of 6.22-32.77 cm 3 / g and an equilibrium adsorption capacity for nitrogen of 1.74-10.9 cm 3 / g at normal temperature and pressure, and the selectivity of IAST (CH4 / N2) is 5.5-7.96.

[0013] Based on the adsorption characteristics of the above porous carbon material, it can be applied to the field of methane-nitrogen adsorption separation technology. For example, it can be applied to the separation and purification of unconventional natural gas, especially suitable for extracting methane or removing nitrogen contained therein from low-concentration coalbed methane, low-saturation natural gas or shale gas.

[0014] Based on an in-depth study of the chemical structure characteristics of carbon precursors during the preparation of porous carbon materials in the prior art and an in-depth understanding of the pore formation mechanism during the preparation of porous carbon, a method for preparing porous carbon materials by a one-step method using aldose compounds as carbon precursors is proposed by selecting aldose compounds as carbon precursors and ingeniously utilizing the chemical structure characteristics of such compounds. When using aldose compounds as carbon precursors, during the high-temperature treatment process, the -C-O-C- group in the aldose compound structure has poor thermal stability and the chemical bond breaks at a relatively low temperature, decomposing to produce CO 2 CO, and H 2 2O gas. The escape of these native gases plays a certain role in pore formation. Especially by adjusting the heating rate and controlling the final treatment temperature and time, it is possible to produce a microporous structure by the breakage of the -C-O-C- group and -OH group in the structure while the aldose compound generally maintains a certain carbon skeleton structure, thereby preparing porous carbon materials. Using aldose compounds as carbon precursors to prepare porous carbon can achieve zero addition of activators, greatly reducing the preparation cost of porous carbon and simplifying the preparation process of porous carbon.

[0015] Therefore, compared with the prior art, the present invention has the following beneficial technical effects:

[0016] (1) According to the characteristics of the chemical structure, a carbon precursor with a -C-O-C- structure is selected, and porous carbon can be directly prepared without physical activation or chemical activation, greatly simplifying the preparation process.

[0017] (2) Compounds with the chemical structure characteristics described in the present invention exist widely and abundantly in nature, such as starch, sucrose, fructose, and cellulose, etc., which greatly reduces the preparation cost of porous carbon.

[0018] (3) Compounds with the chemical structure characteristics described in the present invention generally contain only three elements: carbon, hydrogen, and oxygen, with a simple composition. The pore formation is achieved by the release of CO x . There is no need to use acids or other reagents for post-treatment or pretreatment, and no volatile components that are harmful to the environment and humans will be released. The preparation process is relatively green and safe. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 FIGS. are the BET diagram and pore size distribution diagram of the porous carbon material prepared from cellulose.

[0020] Figure 2 FIG. is the methane-nitrogen adsorption separation diagram of the porous carbon material prepared from cellulose.

[0021] Figure 3 FIGS. are the BET diagram and pore size distribution diagram of the porous carbon material prepared from β-cyclodextrin.

[0022] Figure 4 Methane and nitrogen adsorption separation diagram of the porous carbon material prepared from β-cyclodextrin.

[0023] Figure 5 Selectivity diagram of the two-component separation of the porous carbon material prepared from β-cyclodextrin.

[0024] Figure 6 Methane and nitrogen adsorption diagram of the porous carbon material prepared from L-arabinose.

[0025] Figure 7 Methane and nitrogen adsorption diagram of the porous carbon material prepared from methyl-β-D-ribofuranoside.

[0026] Figure 8 BET diagram of the porous carbon prepared with sodium gluconate as the carbon precursor. Detailed implementation manners

[0027] The following examples are used to illustrate the present invention, but are not used to limit the scope of the present invention.

[0028]

Example 1

[0029] Put 2 g of cellulose powder in a tubular furnace under a nitrogen atmosphere. The heating program of the heating furnace is set to reach 900 °C from room temperature at a rate of 2 °C / min and hold at 900 °C for 1.5 h to obtain cellulose-based porous carbon (Cell-900). Figure 1 BET diagram and pore size distribution diagram of the porous carbon material prepared from cellulose. Figure 2 Methane and nitrogen adsorption separation diagram of the porous carbon material prepared from cellulose. It can be seen that Figure 1 this porous carbon material shows a typical type I adsorption isotherm curve. At the low-pressure region, the N 2 equilibrium adsorption capacity increases sharply. After the micropores are filled, almost no adsorption occurs with the increase of pressure, indicating that the porous carbon material only contains micropores. Use the DFT model to analyze the pore size of the nitrogen adsorption and desorption isotherm (BET) of the cellulose-based porous carbon, and it is found that only micropore sizes exist, which is 0.718 nm. From this, it can be explained that the formation reason of the microporous structure of the cellulose-based porous carbon is that oxygen volatilizes as small-molecule gaseous substances such as carbon dioxide, carbon monoxide, and water. Such a microporous environment is conducive to the adsorption and separation of methane and nitrogen. It can be seen that Figure 2 at 298 K, the equilibrium adsorption capacity of the cellulose-based porous carbon for methane is 31.75 cm 3 / g, and the equilibrium adsorption capacity of nitrogen is 10.45 cm 3 / g; combined with Figure 1 , Figure 2, it can be seen that the cellulose-based porous carbon prepared by direct carbonization of cellulose has uniform pore sizes and can effectively adsorb and separate methane and nitrogen.

[0030]

Example 2

[0031] 1 g of β-cyclodextrin (β-CD) was placed in a tubular furnace under a nitrogen atmosphere. The heating program of the furnace was set to reach 900 °C from room temperature at a rate of 5 °C / min and hold at 900 °C for 1 h to obtain a porous carbon material (βCD-900). Figure 3 is the nitrogen adsorption-desorption isotherm at 77 K for the carbon material prepared from β-cyclodextrin, which is a typical type I adsorption isotherm. The equilibrium adsorption capacity increases sharply in the low-pressure region and hardly adsorbs anymore with the increase of pressure after the micropores are filled, indicating that the porous carbon material only contains micropores. The pore size distribution of the nitrogen adsorption-desorption isotherm (BET) of the β-cyclodextrin-based porous carbon was analyzed by DFT, and it was found that only micropore sizes exist, which is 0.559 nm. Such a microporous environment is very conducive to the adsorption and separation of methane and nitrogen. Figure 4 It can be seen that the equilibrium adsorption capacity for methane is 32.77 cm 3 / g, and the equilibrium adsorption capacity for nitrogen is 10.9 cm 3 / g. To evaluate the separation effect of βCD-900 on methane and nitrogen, Figure 5 the selectivity of IAST was calculated through the Dual-Site-Langmuir freundlich model, and the calculated selectivity of methane and nitrogen was 5.55. Combining (CH4 / N2) with Figure 3 and Figure 4 , it can be seen that the porous carbon prepared by direct carbonization of β-cyclodextrin has uniform pore sizes and can effectively adsorb and separate methane and nitrogen.

[0032]

Example 3

[0033] 1 g of L-arabinose was placed in a tubular furnace under a nitrogen atmosphere. The heating program of the furnace was set to reach 900 °C from room temperature at a rate of 5 °C / min and hold at 900 °C for 1 h to obtain a porous carbon material. Figure 6 It can be seen that the equilibrium adsorption capacity of the directly carbonized L-arabinose-based porous carbon for methane is 19.2 cm 3 / g, and the equilibrium adsorption capacity for nitrogen is 7.9 cm 3 / g.

[0034]

Example 4

[0035] 1 g of methyl-β-D-ribofuranoside was placed in a tube furnace under a nitrogen atmosphere. The heating program of the furnace was set to reach 900 °C from room temperature at a rate of 5 °C / min and hold at 900 °C for 1 h to obtain a porous carbon material, and its adsorption and separation performance for methane and nitrogen was tested. As Figure 7 shown, the equilibrium adsorption capacity for methane at 298 K was 24 cm 3 / g, and the equilibrium adsorption capacity for nitrogen was 8.4 cm 3 / g.

[0036]

Example 5

[0037] 1 g of sodium gluconate was placed in a tube furnace under a nitrogen atmosphere. The heating program of the furnace was set to reach 900 °C from room temperature at a rate of 5 °C / min and hold at 900 °C for 1 h to obtain a porous carbon material. As Figure 8 shown, it was found by BET test that the specific surface area of the prepared carbon material was very small, and the equilibrium adsorption capacity for nitrogen in the low-pressure region was very small, showing a non-microporous structure, which could illustrate the necessity of the oxygen-containing heterocycle of the aldose group.

[0038] Although the present invention has been described in detail above with general descriptions, specific embodiments and experiments, modifications or improvements can be made on the basis of the present invention, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of the present invention claimed.

Claims

1. A method for preparing porous carbon materials from aldose compounds, characterized in that: Using aldose compounds as carbon precursors, the temperature was raised to 400~1000 ℃ at a heating rate of 5℃ / min under an inert atmosphere, kept for 0.5~2 h, and then cooled to room temperature to obtain a porous carbon material.

2. The method according to claim 1, characterized in that: The aldose compound is an oxygen-containing heterocyclic compound having an acetal or hemiacetal structure.

3. The method according to claim 2, characterized in that The oxygen-containing heterocyclic compound is one of glucose, sucrose, fructose, L-arabinose, D-ribose, cyclodextrin, starch, cellulose, aldotrioses, aldotrienes, aldopentose, aldohexose, furfural, cyclohexanolactone, cyclic ether, furan and furan derivatives, pyran and pyran derivatives.

4. The method according to claim 3, characterized in that The furan derivative is any one of methyl-β-D-ribofuranoside and β-D-fructofuranoside.

5. The method according to any one of claims 1 to 4, characterized in that The inert atmosphere is any one of nitrogen atmosphere, argon atmosphere or helium atmosphere; the programmed heating rate is preferably 5 °C / min, the temperature is increased to 900 °C, and the holding time is 2 h.

6. The method according to any one of claims 1 to 4, characterized in that The porous carbon material has uniform micropore distribution, and the pore size distribution is concentrated in the range of 0.5nm-0.8nm.

7. A porous carbon material prepared by the method according to any one of claims 1 to 4, characterized in that: The porous carbon material has an equilibrium adsorption capacity of 6.22-32.77 cm2 for methane at room temperature and pressure. 3 / g, and the equilibrium adsorption capacity for nitrogen is 1.74-10.9cm 3 / g, IAST (CH4 / N2) The selectivity is 5.5-7.

96.

8. The porous carbon material according to claim 7 is used for the adsorption and separation of methane and nitrogen.

9. The porous carbon material according to claim 7 is used for separation and purification of unconventional natural gas.

10. The use according to claim 9, characterized in that: The unconventional natural gas is any one of low-concentration coalbed methane, low-saturation natural gas or shale gas.

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