RU2331468C1 - Method of obtaining nano-porous carbon material - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to obtaining of porous carbon materials with a high specific surface and developed microporosity which can find use as adsorbent and porous carbon carriers for catalysts. The method of manufacturing the nano-porous carbon material includes the preparation of a solid mixture of natural anthracite with a hydroxide of sodium, potassium or lithium by their mixture in a mass ratio 1:5-1:7, melting in preliminary preheating up to temperature of fusion of hydroxide of muffle of furnaces, carbonisation in an atmosphere of gases carbonisation at the temperature 600-800°C, cleaning using water and drying.

EFFECT: simplification and reduction of duration of process of obtaining.

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Description

The invention relates to the field of production of porous carbon materials with a high specific surface area and a developed pore system that can be used as adsorbents for the purification of air, water from mineral and industrial pollution, as well as carriers for catalysts.

Known methods for producing activated carbon (AC) with high values of the specific surface carbonization of fossil fuels under conditions of chemical activation by alkali metal compounds.

When using highly morphized coals and anthracites as carbon raw materials, it is necessary to subject them to preliminary oxidative action to obtain carbon materials with a high specific surface and developed microporosity in order to increase the spatial mobility of the carcass. Subsequent introduction of alkali metals into the organic framework of coal is carried out by treating it with aqueous or alcoholic solutions of the metal hydroxide of the first (Ia) group of the Periodic System. The method of treating coal with metal hydroxides includes the following operations: preparation of alkali solutions of a certain concentration, mixing coal with an alkali solution and keeping the mixture for 72 hours. Then, the samples impregnated with alkali are dried, fractionated and subjected to carbonization in a tubular quartz reactor in an argon stream at temperatures of 600-800 ° C (Yu.V. Tamarkina, V. A. Kucherenko, T. G. Shendrik. Development of the specific surface of natural coal in the presence of potassium hydroxide.// Journal of Chemistry of Chemistry, 2004 .-- T.77. - issue 9. - S.1452-1455).

The disadvantages of this method are the multi-stage and duration of sequential operations, including first an oxidative modification of the structure of coal with an oxidizing agent, and then chemical activation with alkali. In the presence of alkalis, the specific surface develops, but the effect is less, the greater the degree of metamorphism the source coal has, and is minimal for anthracites. In the selected activation modes, the maximum attainable surface for anthracite is not more than 450 m ² / g.

A known method of producing a porous carbon material obtained by direct mixing of natural anthracites with hydroxides MOH (M = K, Na) in a mass ratio MOH / coal = 3 and subsequent thermolysis of the components with a temperature increase from room temperature to 760-730 ° C in an atmosphere of N ₂ and exposure at a final temperature for an hour. The carbonate obtained is washed first with a HCl solution, then with water to a neutral medium, and dried at 110 ° C to constant weight. Thermolysis of anthracites in the presence of alkalis can be considered as the implementation of the carbonization process in the chemical activation mode [M.A. Lillo-Rodenas, D. Losano-Castello, D. Cazorla-Amoros, A. Linares-Solano / Preparation of activated carbons from Spanish anthracite. II. Activation by NaOH // Carbon, 2001 .-- V.39. - P.751-759].

In the known method, the activating effect of alkali on the development of the specific surface and microporous volume is achieved due to the decisive role of gas N ₂ supplied to the reactor at a rate of at least 500-960 ml / min. The disadvantages of this method include the high gas flow rate N ₂ (≥100 l per experiment). In addition, the carbonization process requires special technological equipment - a flow reactor, the manufacture of which requires additional costs. In addition, the carbonaceous feed used as the starting material should be attributed to semi-anthracite rather than anthracite (content C = 82-89 wt.%).

The closest to the proposed method in essence and the final result is a method for producing a nanostructured carbon material from carbon raw materials (coals, petroleum coke) by preliminary oxidation sulfonation with sulfuric acid in the presence of a nitrous acid salt in the cold, dilution with water and heating to hydrolyze the aromatic sulfonic acids. The carbon product treated by this method after filtering off the precipitate is subjected to melting in the presence of metal hydroxides of the first (Ia) group and subsequent carbonization of the resulting melt in an inert or reducing medium formed by carbonization gases at 600-1000 ° C. In the described method, a preliminary chemical modification of the coal structure in reactions with an oxidizing agent (H ₂ SO ₄ -NaNO ₂ ) is used to develop the specific surface, which provides additional formation of new structural fragments and O-, N-, S-containing functional groups. As a result, a significant reorganization of the initial structure of coal is achieved in the entire volume of the coal matrix. During carbonization in the presence of alkali, destruction is accompanied by the formation of a system of new bonds between structural fragments with the formation of a secondary graphite-like structure (RU 2206394, publ. 06/20/2003).

The disadvantage of the described method of obtaining the target product is the use of complex, time-consuming oxidative pretreatment of the feedstock, the implementation of which requires careful adherence to the preparation and implementation of numerous stages for the isolation of intermediate products of oxidation, hydrolysis, substitution reactions, etc. In addition, chemical modification of the feedstock leads to additional costs of reagents, energy, time, which makes this method economically costly and environmentally unsafe due to the released sulfur and nitrogen oxides into the environment. In addition, this method does not apply to the production of nanoporous carbon materials from anthracites.

The objective of the present invention is:

- to simplify and reduce the duration of the process of obtaining nanoporous carbon materials by eliminating the stage of preliminary oxidative treatment of the feedstock;

- in expanding the range of carbon raw materials through the use of natural anthracite.

The problem is solved in that in the proposed method for producing nanoporous carbon material, comprising melting a mixture of carbon raw materials with metal hydroxide (Ia) of the group of the Periodic system, followed by carbonization of the obtained melt in an atmosphere of exhaust gases at a temperature of 600-800 ° C, washing the product with water from impurities inorganic components and drying, according to the invention, natural anthracite is used as the carbonaceous feed, and its mixture with sodium, potassium, lithium hydroxide is taken in mass Ocean 1: 5-1: 7, is melted in a furnace preheated to the melting point of the metal hydroxide.

A comparative analysis of the invention shows that, in contrast to the prototype, natural anthracite is used as the starting carbon-containing material. In addition, a distinctive feature of the prototype is the combination of the melting procedure of a mixture of anthracite and alkali in order to ensure migration mobility of the hydroxide and subsequent carbonization. In the prototype, these operations are divided, first the preliminary procedure of melting the oxidation product with alkali is carried out in order to decompose the oxidation products (sulfonic acids) and obtain phenolates, and then the resulting melt is placed in the furnace for subsequent carbonization. In addition, unlike the prototype in the present invention, the furnace is preheated to the melting point of metal hydroxide, where then both melting and carbonization are carried out.

Thanks to these distinctive features, it was possible to greatly simplify and reduce the duration of the process of obtaining nanoporous carbon material by eliminating the many-hour chemical treatment of carbon material, as well as expanding the range of source fossil raw materials through the use of natural anthracites. The proposed method is simple to implement, quite economical, does not require complex technological equipment.

The method is confirmed by specific examples.

Example 1 (prototype)

Natural anthracites are used as the initial carbonaceous feed (see Table 1). 1 g of Siberian anthracite (AS), ground to a fraction of 0.16-0.25 mm, is mixed with 18 ml of concentrated sulfuric acid. 2.704 g of potassium nitrite are added gradually to the resulting suspension, while stirring and cooling the mixture with ice. The mixture is gradually heated until the evolution of nitrogen oxides ceases, diluted with water and boiled until the hydrolysis of the aromatic sulfonic acids formed ends. Evaporated in 1/3 of the volume of the mixture after cooling to room temperature, is filtered off, the precipitate is washed to a neutral pH of the wash water.

The filter cake was first mixed with 4.67 g of crystalline potassium hydroxide, and then after evaporation of the water, the mixture was melted to decompose aromatic sulfonic acids and obtain phenols of the corresponding metals until gas evolution ceased. The resulting melt is subjected to further carbonization in a reducing medium of exhaust gases in a muffle furnace to a temperature of 700 ± 50 ° C with an exposure of 10 minutes at a final temperature. Then the crucible is removed from the muffle, cooled to room temperature, and the carbonate is washed from alkali and alkali metal impurities with room temperature water, acidified with water, again with water to a neutral environment. The resulting sample is first dried in air to a free-flowing state, then finally dried in an oven at a temperature of 102-105 ° C. The specific surface was measured on a Sorbtometr-4 apparatus and evaluated by nitrogen adsorption at 77K by the BET method after preliminary training of the sample at 300 ° C for 4 hours. S _BET for this sample was 840 m ² / g (see table 2).

Example 2

5 g of anthracite AC are mixed with 25 g of crystalline potassium hydroxide, the mixture is placed in a crucible with a lid and melted in a muffle furnace previously heated to the melting temperature KOH (T _KOH = 360 ° C) for 10 minutes. The resulting AC-KON melt is subjected to further carbonization in the exhaust gas reducing atmosphere, raising the furnace temperature to 600 ° C. Then the crucible is removed from the muffle, cooled to room temperature, and the carbonate is washed from alkali and alkali metal impurities with room temperature water, acidified water, hot water to a neutral environment. The resulting sample is first dried in air to a free-flowing state, then finally dried in an oven at a temperature of 102-105 ° C. The specific surface area of the carbon sample S _BET was 1057 m ² g

Example 3. Obtaining active carbon is carried out according to the method described in example 2, but thermolysis of the solid mixture "AC-KON" to a temperature of 800 ° C. S _{BET of the} obtained carbon sample was 2568 m ² / g, pore diameter 1.73 nm. The development of the porous structure occurs gradually as a result of decomposition of surface alkaline complexes (salts), which are active centers of gasification.

Example 4. Obtaining an active carbon product is carried out according to the method described in example 3, but carry out the carbonization of the mixture "AC-KON" to a temperature of 800 ° C with exposure of the sample for 1 hour. S _{BET of the} obtained carbon sample was 2350 m ² / g, pore diameter 1.82 nm. The development of microporous volume occurs against the background of simultaneously occurring carbonization reactions and the gasification process with volatile pyrolysis gases. An increase in the duration of the thermolysis of the AS-KON system from 15 minutes to 1 hour leads to a decrease in the yield of the final thermolysis product due to the intensification of the process of burning active carbon, as well as to a certain decrease in Ssp., Possibly due to shrinkage.

Example 5. It differs from example 3 in that the mass ratio of AC: KOH is taken to be 1: 3. The resulting product has S _BET equal to 1189 m ² / g, pore volume 0.572 cm ³ / g A decrease in the lower limit of the ratio of coal to alkali reduces the degree of development of the porous structure in coal due to a decrease in the concentration of the “anthracite-KOH” surface complexes that activate the formation of volatile thermolysis products, and the required reaction depth is not achieved.

Example 6. Obtaining active carbon is carried out according to the method described in example 3, but the mass ratio of AC: KOH is taken to be 1: 7. S _{BET of the} obtained carbon sample was 2870 m ² / g, pore volume 1.25 cm ³ / g. Under these conditions, the maximum development of the porous structure is achieved due to the fact that in the pyrolysis gases the content of gaseous products (H ₂ , CO ₂ , CO) sharply increases due to the reactions of KOH with polyarene fragments of the carbon skeleton. Excess introduced hydroxide promotes the development of a porous structure due to the additional pore-forming action of CO and CO ₂ released as a result of reactions of KOH transformation products (K ₂ CO ₃ and, possibly, K ₂ O) with carbon.

Example 7. It differs from example 3 in that solid NaOH is used as the metal hydroxide of the (Ia) group. The dry mixture “AC-NaOH” prepared by physical mixing is melted in a muffle cabinet preheated to the melting temperature of NaOH (T _NaOH = 320 ° C) for 10 minutes. A carbon product is obtained having an S _{BET of} 1100 m ² / g. The development of the microporous structure to a certain extent depends on the nature of the cation of the introduced alkali, since under the same conditions of thermolysis of the "anthracite-MON, M = K, Na" system, the rate of formation of volatile products, especially CO ₂ , is higher for KOH samples than for Na-samples, which means that the number of surface complexes formed is higher in the case of KOH than with NaOH.

Example 8. Obtaining active carbon is carried out according to the method described in example 7, but thermolysis of the solid mixture "AC-NaOH" is carried out to a temperature of 600 ° C, keeping the sample for 15 minutes. The S _BET value of the obtained carbon sample was 272 m ² / g. The weak development of the microporous volume (Vmicro = 0.07 cm ³ / g) is probably due to the fact that in the presence of NaOH the formation of active surface complexes on coal particles is difficult, in the case of KOH they form at a higher rate and at a lower temperature.

Example 9. It differs from example 7 in that solid LiOH is used as the metal hydroxide of the (Ia) group. The physical mixture "AC-LiOH" is placed in a muffle heated to 460 ° C (mp. LiOH). The resulting product has an S _{BET of} 235 m ² / g. During the thermolysis of the anthracite-LiOH system, the smallest effect of the interaction of Li ⁺ , OH ^- , LiOH with fragments of the carbon skeleton is achieved, while the depth of the activating effect of alkalis increases in the order LiOH <NaOH <KOH.

Example 10. It differs from example 3 in that Ilovaysky anthracite, a fraction of 0.25 mm, is used as the source coal. The target product resulting from the thermolysis of the IA-KON system has a lower S _BET value = 1526 m ² / g compared to the carbon product from the IA sample. Under similar experimental conditions, the content of mineral impurities in the initial coal affects the characteristics of the final product. The high porosity of the final product from the AS sample is probably consistent with the pore-forming effect of gaseous products initiated by the decomposition of carbonates from impurities (CaCO ₃ and others).

Example 11. Obtaining active carbon is carried out according to the method described in example 10, but solid NaOH is used as the metal hydroxide of the (Ia) group. The resulting product has an S _{BET of} 2547 m ² / g, exceeding the Ssp values obtained under similar conditions for AS, probably due to the higher content of O-containing functions in the initial angle (see Table 1). The greater the number of O-containing functional groups, the greater the porosity of the carbonization product. Changes caused by the action of alkalis are determined both by the nature of the hydroxide and the nature of anthracite, therefore, the treatment of different anthracites under identical conditions leads to the formation of activated carbons with different structural characteristics.

Thus, the present invention can significantly reduce the duration and number of stages of the process of obtaining nanoporous carbon material from coal, as well as expand the range of raw fossil raw materials through the use of hard-activated natural anthracites.

Table 1 Characterization of initial anthracite samples No. Sample Elemental analysis, wt.% Ash content,% C, ^daf H, ^daf N, ^daf S, ^daf O ^daf one Siberian Anthracite (AS) 95.69 1.85 1.35 0.27 0.84 3,50 2 Ilovaiskaya Anthracite (IA) 92.06 3.23 1.78 0.48 2.41 3.27

table 2 Production conditions and texture characteristics of carbon materials No. Sample Mass ratio, g × g ^-1 Temperature ° C Surface S _BET , m ² / g Pore volume, cm ³ / g one AC / KON (prototype) 1: 5 730 840 0.383 2 AC / KON 1: 5 600 1057 0.427 3 AC / KON 1: 5 800 2568 1,126 four AC / KON 1: 5 800 2350 1,035 5 AC / KON 1: 3 800 1189 0.572 6 AC / KON 1: 7 800 2870 1,254 7 AC / NaOH 1: 5 800 1104 0.495 8 AC / NaOH 1: 5 600 272 0.242 9 AC / LiOH 1: 5 800 235 0,098 10 IA / CON 1: 5 800 1526 0.700 eleven IA / NaOH 1: 5 800 2547 1,178

Claims (1)

A method of producing a nanoporous carbon material, comprising melting a mixture of carbon raw materials with metal hydroxide (Ia) of the group of the Periodic system, followed by carbonization of the obtained melt in the atmosphere of exhaust gases at a temperature of 600-800 °, washing the product with water from impurities of inorganic components and drying, characterized in that natural anthracite is used as the carbonaceous feed, and a mixture of it with sodium, potassium and lithium hydroxide is taken in a mass ratio of 1: 5-1: 7, it is melted in an oven, the pre but heated to the melting point of the metal hydroxide.