RU2311227C1 - Method of production of the nanostructure carbonic material with the high specific surface and microporosity - Google Patents

Abstract

FIELD: chemical industry; gas-processing industry; other industries; methods of production of the nanostructure carbonic material with the high specific surface and the microporosity.

SUBSTANCE: the invention is pertaining to the method of production of the porous carbonic material and may be used in the capacity of the sorbents for the energetic gases (the natural gas, hydrogen and other gases) and the toxic gases, and also in other fields of the science and engineering. The method provides for carbonization of the lignocellulose material with the ash content of 8-20 mass %, the subsequent alkaline activation in the presence of the carbonates and-or sodium) or potassium hydroxides and washing. At that the carbonization is exercised at the temperature of 400-800°C at the molar ratio of the atmospheric oxygen to carbon pf the lignocellulose material equal to 0.8-3.0 within 1-60 seconds in the boiling layer of the catalyst or the inert carrier. The alkaline activation is exercised at the temperature of 600-1000°C in the inert or reducing atmosphere, and the washing of the product after the activation is exercised using the acid solution. The technical result of the invention consists in production of the nanostructure carbonic materials with the higher values of the specific surface and the total volume of the pores and the volume of the micropores at the price reduction of the production process.

EFFECT: the invention ensures production of the nanostructure carbonic materials with the higher values of the specific surface and the total volume of the pores and the volume of the micropores at the production process price reduction.

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Description

The invention relates to the production of porous carbon materials, in particular to the production of biomass from lignocellulosic raw materials, for example, plant waste products of activated carbon materials having a high specific surface area and microporosity. The invention may find application as sorbents for energy (natural gas, hydrogen, etc.) and toxic gases, as well as in other fields of science and technology.

Known methods for producing porous carbon materials by pyrolysis of solid organic materials, including various types of coals, oil residues, biomass waste, followed by their activation with carbon dioxide and / or water vapor and / or oxygen (VB Fenelonov. Porous Carbon / Novosibirsk, 1995, 513 pp.). During activation, the removal of bound water, volatile hydrocarbons, as well as the interaction of carbon with activating agents with the formation of hydrogen and carbon oxides and the formation of a porous structure.

Known methods for producing porous carbon materials such as activated carbons, which are obtained by activation of mineral catalysts introduced into the starting material, for example, Friedel-Crafts catalysts — ZnCl ₂ , AlCl ₃ , H ₃ PO ₄ , or redox catalysts — salts or alkali and alkali oxides earth metals. (Whitekurst D.D., Mitchell T.O., Farkashi K. Coal liquefaction. - M .: Mir. - 1986. - p. 256; U.S. Patent 6537947, IPC B01J 020/02, priority 25.03.2003, McKee DW Fuel. - 1983. - v. 63. - p. 170; U.S. Patent 6,030,922 СВВ 031/10, priority 29/02/2000). The latter type of catalyst is usually used in the presence of an oxidizing gas (H ₂ O, CO ₂ , air) at 500-900 ° C. Using these methods, it is possible to obtain activated carbon with S _beats. - not more than 850 m ² / g and micropore fractions - not more than 25%.

The main disadvantage of the known methods is the impossibility of producing nanostructured carbon with a high specific surface (3000-4000 m ² / g calculation by nitrogen adsorption isotherms at 77 K by the BET method) and a high proportion (up to 90%) and volume (1.5-2.0 cm ³ / g) micropores.

Known methods for producing porous carbon materials by oxidizing, for example, humus coals, or their cokes, or petroleum cokes with nitric acid or sulfuric acid with the addition of nitrous acid salts (US Patent 4082694, B01J 21/18, C01B 31/08, C01B 31/12 , priority 04.04.1978; RF Patent 2206394 C1 B01J 20/20, C01B 31/12, priority 20.06.2003). As a result, the formation of aromatic acids, polyhydric carboxylic (naphthoic) and polyhydric polycarboxylic acids (coke) is assumed. The resulting mixture of acids is mixed in a solvent with a metal hydroxide of the first (Ia) or second (IIa) group of the Periodic System and is subjected to activation in an inert atmosphere. Before activation, the solvent is first removed by evaporation at a slow temperature increase. The optimum activation temperature is 700-800 ° C. The resulting product is washed from metal salts of the first (Ia) or second (IIa) group, dried in air, and then, if necessary, subjected to controlled oxidative activation of carbon dioxide. As a result, adsorbents with a specific surface above 2000 m ² / g and a micropore volume of not more than 1.2 cm ² / g are obtained.

The disadvantage of this method is the use of dilute nitric and sulfuric acids in it, which leads to the formation of a large number of nitrogen and sulfur oxides that are harmful to the environment.

A known method of producing porous carbon materials from lignocellulosic raw materials by the example of rice husk (Yu. Guo, K. Yu, Z. Wang, H. Xu, Carbon, 41 (2003), p.1645-1648). Pyrolyzed rice husk is activated with alkalis or potassium or sodium carbonates at 650-800 ° C in an inert atmosphere for 0.5-2 hours. After that, the resulting product is washed with water and dried at 120 ° C. The carbon material had a specific surface area of not more than 3000 m ² / g and a micropore volume of not more than 0.64 cm ³ / g. In addition, the use of alkali metal carbonates did not lead to a significant development of the specific surface and the formation of micropores.

Closest to the proposed technical solution, which is taken as a prototype, is a method for producing activated carbon materials by two-stage activation of lignocellulose-containing material, including waste from wood processing (bark, sawdust, wood chips, etc.) and crop production (nutshell, fruit seeds, etc.). .p.) (US Patent 5416056, С01В 031/12; B01J 020/20, priority 05.16.1995).

The first stage is the carbonization of the lignocellulosic precursor with phosphoric acid (H ₃ PO ₄ ) at a temperature of 150-590 ° C (optimal temperature is 430-530 ° C). The carbon-containing precursor is mixed with a solution of H ₃ PO ₄ with an acid / carbon ratio of from 0.5: 1 to 3: 1 (preferred ratio of 1: 1 to 2: 1). After removal of the solvent by evaporation, the mixture is carbonized at appropriate temperatures for 0.5-1.5 hours, followed by washing the carbonized material to remove phosphoric acid. The second stage of the process is the activation of the obtained carbonized material by a metal compound (potassium hydroxide) at a temperature of 650-980 ° C (optimal temperature is 760-930 ° C). The carbon material is treated with a KOH solution with a ratio of 0.5: 1 to 4: 1. Before activation, the solvent is removed by slowly raising the temperature. Activation is carried out for 4 hours in an inert atmosphere, followed by washing with hot water (80 ° C) to a pH of 7.5 and drying at 110 ° C. As a result, carbon materials were obtained with a specific surface area of not more than 2500 m ² / g, a pore volume of less than 1.4 cm ³ / g, a micropore volume of less than 1.0 cm ³ / g and a micropore fraction of less than 80% (d _pores <2 nm).

The disadvantage of this method is the complicated procedure for obtaining, the use of a large amount of liquid acidic and alkaline waste. In addition, the method selected as a prototype, does not allow to obtain nanostructured carbon materials with a specific surface area of more than 2500 m ² / g and a micropore volume of more than 1 cm ³ / g

The authors were tasked with developing a cheaper and environmentally friendly method for producing a nanostructured carbon material with a high specific surface area and microporosity from lignocellulosic biomass waste, including crop waste (husk of rice, oats, wheat straw and other cereals) and wood processing (sawdust, wood dust )

The problem is solved in that in a method for producing a nanostructured carbon material with a high specific surface area and microporosity, including carbonization of lignocellulosic material with an ash content of 8-20 wt.%, Subsequent alkaline activation in the presence of carbonates and / or sodium or potassium hydroxides and washing, according to the invention that carbonization is carried out at 400-800 ° C with a molar ratio of air oxygen to carbon of lignocellulosic material equal to 0.8-3.0 for 1-60 seconds in a fluidized bed of catalyst and and an inert carrier, an alkaline activation is carried out at 600-1000 ° C in an inert or reducing atmosphere, and washing the product after activation of the acid solution is carried out. In this case, as a catalyst, either metal oxides d-elements of the 4th and 5th periods of the Periodic system deposited on oxide supports are used, or their combinations with each other and with metal oxides of the 3rd period of the Periodic system. Moreover, during alkaline activation, carbonates and / or hydroxides are introduced when their molar ratio to carbon is 0.7-4.0, activation is carried out within 0.25-4.0 hours, and the heating rate to the activation temperature is 1-20 degrees ./min

The technical effect of the proposed method is to obtain nanostructured carbon materials with higher values of specific surface area, total pore volume and micropore volume, in the prostate and the speed of carbonization of lignocellulosic raw materials without the use of additional reagents, as well as the possibility of carbonization in automatic mode, which makes it possible to reduce the cost of the process of obtaining nanostructured carbon materials in general.

Figure 1 presents the principal scope of the process of obtaining nanostructured carbon material. Figure 2 presents a high resolution photograph of nanostructured carbon, explaining the structure of the obtained carbon materials with S _beats. = 3360 m ² / g, V _Σ = 2.18 cm ³ / g, V _μ = 1.87 cm ³ / g.

The inventive method is carried out by two-stage processing of lignocellulosic raw materials (Figure 1), including the primary carbonization of biomass either by pyrolysis in an inert atmosphere, or by partial oxidation in a fluidized bed of either a catalyst, or an inert carrier with atmospheric oxygen, followed by activation by metal compounds of either the first (Ia) or the second (IIa) group of the Periodic system, or a combination thereof.

The initial biomass, if necessary, is ground to a size of 2-5 mm. The carbonization of carbon-containing raw materials is carried out either by pyrolysis in an inert or reducing atmosphere at 300-650 ° C for 0.5-5 hours, or gasification (partial oxidation) in a fluidized bed of catalyst or inert support at a temperature of 400-800 ° C with a contact time of 0 , 1-60 seconds and α = 0.8-3.0 (α is the ratio of O ₂ air to carbon). The optimal conditions for pyrolysis are a temperature of 400-450 ° C, maintained for 2-3 hours in a stream of nitrogen. Gasification is preferably carried out in a fluidized bed of catalyst at a temperature of 450-600 ° C with a contact time of 0.9-1.5 seconds and α ~ 1.

It should be noted that the carbon materials obtained after the first stage do not have any pronounced microporous structure.

Further, carbon materials are treated with a solution of metal compounds of either the first (Ia) or second (IIa) groups of the Periodic system, or a combination of them in a ratio of 50-100 mol / kg, optimally 70 mol / kg. The resulting mixture is first evaporated at 110-120 ° C, then subjected to activation at a temperature of 600-1000 ° C, preferably at 750-900 ° C, either in an inert or in a reducing atmosphere of hydrogen or gases formed during the pyrolysis and the interaction of carbon with hydroxides metals of the first (Ia) or second (IIa). The activation product is washed with acid solutions, water to a neutral medium to ensure complete removal of metal compounds contained in the form of trace elements in the original lignocellulosic raw materials. The washed residue is dried at 100-120 ° C to constant weight.

The resulting product is a nanostructured carbon material with a high specific surface (2500-4000 m ² / g), pore volume (2-3 cm ³ / g) and a high proportion of microporosity up to 90% (pore size less than 2 nm).

Such a surface can have only graphite-like monolayer particles (graphenes) of nanometer sizes with a cell-like structure of individual cells, consisting of two to three graphenes, which is confirmed by a high resolution photograph (Figure 2) (magnification 3,116,000 x). (VB Fenelonov. Porous carbon. Novosibirsk, 1995, p. 453).

The inventive method is characterized by a simpler and faster way to conduct the stage of carbonization without the use of additional reagents such as phosphoric acid and the formation of acidic liquid waste. In this case, gasification in a fluidized bed is exothermic, which makes it possible to implement a non-volatile method for producing nanostructured carbon materials. Obtained by the proposed method, carbon materials have higher values of specific surface area, total pore volume and micropore volume.

Specific surface measurements were performed on an ASAP-2400 (Micrometrics) setup for nitrogen adsorption at 77 K after preliminary training of the samples at 300 ° C and a residual pressure of less than 0.001 mm Hg. until gas evolution ceases without contact with the atmosphere after training. Nitrogen adsorption isotherms were measured in the relative pressure range from 0.005 to 0.995 atm and their standard processing with calculation of the total surface by the BET method, micropore volume (with a size less than 2 nm) and the surface of the mesopores remaining after micropore filling (see S. Gregg, K . S.V. Sign. Adsorption, specific surface, porosity. Mir, M., 1984). The invention is illustrated by the following examples.

Example 1

20 g of rice husk (lignin content - 15 wt.%, Cellulose - 31%, ash - 19%) is pre-pyrolyzed in a static reactor at 400 ° C for 2 hours in a stream of nitrogen (nitrogen flow rate - 5 l / h). After cooling, carbonized carbon material (11 g) is mixed with a KOH solution (44 g or 72 mol / kg, which corresponds to a KOH / C molar ratio of 1.31) and, after evaporation of water, is placed in a static reactor for further activation. The mixture is heated in a stream of inert gas (nitrogen) to 400 ° C at a rate of 10 ° C / min, incubated for 20 minutes and then heated at a speed of 15 ° C / min to 800 ° C and maintained at this temperature for 2 hours. After cooling, the carbonizate is washed with water heated to 80 ° C, then with an acid solution, then with water to a neutral medium. The resulting product is dried in an oven at a temperature of 110-120 ° C to constant weight. The yield of the nanostructured carbon composite is 30%. The specific surface (S _beats ), the pore volume is estimated by nitrogen adsorption by the BET method, and it is 2600 m ² / g, the total pore volume (V _Σ ) is 1.53 cm ³ / g with a micropore fraction of 81% (V _μ = 1 24 cm ³ / g).

Example 2

It differs from Example 1 in that wheat straw is used as the initial lignocellulosic raw material (lignin content - 10 wt.%, Cellulose - 40%, ash - 8%). Pyrolysis is carried out at 500 ° C for 3 hours in a reducing environment created by pyrolysis gases. Carbonated carbon material (10 g) is mixed with a solution of KOH and K ₂ CO ₃ (35 g KOH and 45 g K ₂ CO ₃ or a total of 95 mol / kg, which corresponds to a molar ratio KOH / C = 1.52). With further activation, the mixture is heated in a reducing medium (volume mixture N ₂ / H ₂ = 4/1) to 450 ° C at a rate of 8 ° C / min, incubated for 40 minutes and then heated at a speed of 20 ° C / min to 750 ° C and incubated at this temperature for 3 hours. Final yield 40%. S _beats = 2550 m ² / g, V _Σ = 1.77 cm ³ / g, V _μ = 1.51 cm ³ / g, the proportion of micropores is 85%.

Example 3

It differs from example 1 in that the preliminary carbonization of the rice husk is carried out in a fluidized bed reactor of a supported copper-chromium catalyst of the following composition: 1.75% (weight) CuO + 3.5% MgO + 6.5% Cr ₂ O ₃ , deposited on γ-Al ₂ O ₃ at a temperature of 450 ° C, with a contact time of 2.5 seconds and α ~ 1.5. Activation is carried out at 600 ° C for 4 hours. The heating rate to the activation temperature is 1 ° C / min. During carbonization, a supported copper-chromium catalyst of the following composition is used: 1.75% (wt.) CuO + 3.5% MgO + 6.5% Cr ₂ O ₃ supported on γ-Al ₂ O ₃ . The final yield of 25%. S _beats = 2960 m ² / g, V _Σ = 1.8 cm ³ / g, V _μ = 1.62 cm ³ / g, the proportion of micropores is 90%.

Example 4

Differs from example 3 in that the carbonization in a fluidized bed is carried out at a temperature of 500 ° C, with a contact time of 1 sec and α ~ 2.5. The activation temperature is 800 ° C, the heating rate is 10 ° C / min. The final yield of 25%. S _beats = 3360 m ² / g, V _Σ = 2.18 cm ³ / g, V _μ = 1.87 cm ³ / g, the proportion of micropores is 86%.

Example 5

It differs from Example 4 in that oat husk is used as the initial lignocellulosic raw material (lignin content is 12 wt.%, Cellulose is 35%, ash content is 10%). Carbonization is carried out in a fluidized bed of an inert carrier (river sand). The final yield of 30%. S _beats = 2930 m ² / g, V _Σ = 1.83 cm ³ / g, V _μ = 1.57 cm ³ / g, the proportion of micropores is 86%.

Example 6

It differs from example 4 in that the carbonization is carried out in a fluidized bed of iron-manganese catalyst, the following composition: 1.25% (wt.) Fe ₂ O ₃ + 1.25% MnO ₂ deposited on γ-Al ₂ O ₃ . The alkaline activation of carbonated material is carried out at a final temperature of 900 ° C. Yield 20%. S _beats = 3210 m ² / g, V _Σ = 2.97 cm ³ / g, V _μ = 1.48 cm ³ / g, the proportion of micropores is 50%.

Example 7

Differs from example 4 in that the alkaline activation of the carbonized material is carried out at a final temperature of 750 ° C. Yield 28%. S _beats = 3450 m ² / g, V _Σ = 2.01 cm ³ / g, V _μ = 1.68 cm ³ / g, the proportion of micropores is 84%.

Example 8

It differs from example 4 in that the carbonization in a fluidized bed is carried out at a temperature of 600 ° C, with a contact time of 10 seconds and α ~ 1. Carbonated carbon material (15 g) is mixed with a solution of KOH and NaOH (ratio of KOH / NaOH = 2: 1, 50.4 g of KOH and 18 g of NaOH in the amount of 90 mol / kg, corresponds to a molar ratio of KOH + NaOH / C = 0, 7). The resulting mixture is activated by passing a mixture of nitrogen and hydrogen in a ratio of 4: 1 by volume (total flow 5 l / h). The final yield of 21%. S _beats = 3910 m ² / g, V _Σ = 2.86 cm ³ / g, V _μ = 1.93 cm ³ / g, the proportion of micropores is 68%.

Example 9

It differs from Example 1 in that birch sawdust is used as the initial lignocellulosic raw material (lignin content - 20 wt.%, Cellulose - 41%, ash content - 0.4%). Final yield 40%. S _beats = 1850 m ² / g, V _Σ = 1.2 cm ³ / g, V _μ = 0.71 cm ³ / g, the proportion of micropores is 59%.

Example 10

It differs from example 4 in that the carbonization is carried out in a fluidized bed of catalyst at a temperature of 400 ° C, with a contact time of 60 seconds and α ~ 0.8. Carbonated carbon material (15 g) is mixed with 110 g of NaOH, which corresponds to 260 mol / kg or molar ratio of NaOH / C = 4.0). The activation temperature is 1000 ° C, the heating rate is 15 ° C / min. After reaching the activation temperature, the mixture was alloyed for 0.25 hours. The final yield of 41%. S _beats = 2850 m ² / g, V _Σ = 2.55 cm ³ / g, V _μ = 1.47 cm ³ / g, the proportion of micropores is 58%.

Example 11

It differs from Example 4 in that carbonization is carried out in a fluidized bed of an inert carrier (river sand) at a temperature of 800 ° C with a contact time of 1 second and α ~ 3.0. The final yield of 25%. S _beats = 2380 m ² / g, V _Σ = 1.54 cm ³ / g, V _μ = 1.2 cm ³ / g, the proportion of micropores is 78%.

As can be seen from the above examples, the proposed method allows to obtain from lignocellulosic material by carbonization (pyrolysis or gasification in a fluidized bed) and activation of a nanostructured carbon material with a high specific surface area and microporosity.

The material obtained by the proposed method can be widely used as an sorbent, as well as a carrier for various types of catalysts.

Claims (5)

1. A method of producing a nanostructured carbon material with a high specific surface and microporosity, including the carbonization of lignocellulosic material with an ash content of 8-20 wt.%, Subsequent alkaline activation in the presence of carbonates and / or sodium or potassium hydroxides and washing, characterized in that the carbonization is carried out at 400-800 ° C with a molar ratio of air oxygen to carbon of lignocellulosic material equal to 0.8-3.0, for 1-60 s in a fluidized bed of catalyst or inert carrier, alkaline activation pour at 600-1000 ° C in an inert or reducing atmosphere, and washing the product after activation is carried out with an acid solution. 2. The method according to claim 1, characterized in that the catalyst is either used on oxide carriers of metal oxides of d-elements of the 4th and 5th periods of the Periodic system, or their combination with each other and with metal oxides of the 3rd period of the Periodic system. 3. The method according to claim 1, characterized in that during alkaline activation, carbonates and / or hydroxides are introduced at a molar ratio to carbon of 0.7-4.0. 4. The method according to claim 1, characterized in that the activation is carried out within 0.25-4.0 hours 5. The method according to claim 4, characterized in that the heating rate to the activation temperature is 1-20 degrees / min.

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