RU2429194C2 - Method of producing cellular graphite - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: coal tar pitch undergoes graphitation in the presence of a catalyst at temperature 600-1000°C. The catalyst used is nanoparticles of iron, cobalt, nickel or mixture thereof, and said particles are deposited on nanostructured carbon material. Graphitation is carried out in a reducing medium, i.e. in the medium of exhaust gases, or in an inert medium.

EFFECT: invention enables graphitation of carbon material at low temperatures.

3 cl, 7 dwg, 10 ex

Description

The invention relates to methods for producing carbon-graphite materials, in particular to the production of penografite, which can be used in the manufacture of flexible foil, anode masses of aluminum electrolytic cells, gaskets, as sorbents for water purification, collection of oil products, etc.

There are various methods for producing penografit by various methods of oxidizing graphite, including by electrochemical treatment of graphite particles in an aqueous solution of nitric acid, followed by washing with water, drying and heat treatment. Electrochemical treatment is carried out at a constant anode potential with an electricity supply of at least 50 mA · h / g of graphite in one or more stages in an aqueous solution of nitric acid with a concentration of 20-58% (RU 2233794, СВВ 31/04, С25В 1/00, 10.08 .2004). The resulting penografit is characterized by a homogeneous structure, bulk density of 1.0-5.0 g / l and a foaming temperature of 150-900 ° C.

Known methods for producing foamed graphite from oxidized graphite in devices with gas burners, in accordance with which fuel gas is burned in a gas burner, mixed with air and oxidized graphite. In this case, gas combustion and its mixing with oxidized graphite can occur in an injector type device (RU 2240282, C01B 31/04, November 20, 2004), due to which the heat transfer rate increases, which increases the quality of penografite.

The disadvantage of the considered methods is the use of graphite as a feedstock with its subsequent various treatments, which were mentioned above.

The present invention allows to abandon graphite as a feedstock, and proposes to use coal tar pitch, which, as you know, has nothing to do with graphite. And crystallization (graphitization) is carried out simultaneously with foaming, i.e. at a low temperature and at the same time eliminate the possible release of benzopyrene into the environment, which, as will be shown below, is always in coal tar pitch, despite all kinds of attempts to improve the pitch.

Graphitization is a physical process (crystallization), which, according to individual authors, can be divided into homogeneous and heterogeneous. The graphitization of “non-graphitizable carbon materials” or difficult-to-graphite materials is heterogeneous. The fact is that “non-graphitized carbon materials” do not exist, and any carbon material can be programmed. Hard-to-graphitized materials require heating to 3000-3200 ° C (first, carbon is evaporated, and then it is condensed) and a preliminary significant compaction of the starting material (soot, charcoal). Easily graphitized materials are graphitized in the range 2200-2800 ° С (V.N. Krylov, Yu.N. Vilk. Carbon-graphite materials and their application in the chemical industry. Chemistry. 1965. 148 pp.). The temperature of graphitization can be lowered, for example, to 1900 ° C, using vanadium as a catalyst (E.V. Novikov, E.A. Belenkov, E.M. Beitinger. Effect of vanadium oxide additives on the graphitization process of coke-pitch carbon materials Bulletin of the Chelyabinsk Scientific Center, issue 3 (16), 2002). The use of nanoparticles of various metals can further reduce the crystallization temperature of the carbon material.

In the application US 2007/0265162, B01J 23/02, 15.11.2007, a method for synthesizing a nanostructured carbon material from a carbon precursor (an aromatic substance consisting of one or two rings and having functional groups such as COOH, C = O, OH, C = C, SO ₃ , NH ₂ , SOH, N = C = O) using catalytic template nanoparticles. Carbon nanostructures are formed around a variety of nanoparticles used as a base. Catalytic nanoparticles work both as nucleation centers for a carbon nanostructure and as catalysts during the carbonization and / or polymerization of a carbon precursor. The resulting nanostructured carbon material has a high specific surface, high porosity and a high degree of graphitization. In the General case, the method consists of 4 stages:

1 - the formation of metal nanoparticles, for this purpose, metal powder (iron, cobalt, nickel, etc.), acid (citric) and water are stirred for 7 days;

2 - the formation of intermediate carbon nanostructures, where the solution prepared in the first stage is mixed with the precursor (an aromatic substance consisting of one or two rings and having functional groups, such as: COOH, C = O, OH, C = C, SO ₃ , NH ₂ , SOH, N = C = O) and the resulting paste is polymerized at 80-90 ° C for 3.5 hours;

3 - carbonization of intermediate carbon nanostructures with the formation of a combined nanostructure, during which the second stage product is filtered off, dried and carbonized in a stream of nitrogen at 1150 ° C for 3 hours or at 850 ° C for 4 hours;

4 - removal of metal nanoparticles from a combined nanostructure, where the composite mixture is treated sequentially with HNO ₃ for 6-8 hours, with a mixture of H ₂ O / H ₂ SO ₄ / KMnO ₄ at 90 ° C for 3 hours and water, followed by drying.

The formation of metal nanoparticles is realized using a dispersing agent (this is an organic molecule that contains one or more functional groups). The dispersant molecule forms a complex with catalyst atoms. When mixed with a carbon precursor, metal nanoparticles provide nucleation sites where carbonization and / or polymerizations can begin or develop. The dual role of metal nanoparticles makes it possible to dispense with the separate addition of template nanoparticles and a catalyst, which eliminates the undesirable functioning of the catalyst atoms as nucleation centers and ensures the formation of a homogeneous carbon nanostructure. That is, it is assumed that due to the formation of a complex of a metal nanoparticle with a precursor during subsequent carbonization at a temperature of 850-1150 ° C, crystallization of nanoparticles of carbon material occurs.

In the application US 2005/0008562, 01B 31/02, 01/13/2005 describes a method for the synthesis of crystalline nanostructured carbon material with a high specific surface area. In a first step, the carbon precursor is mixed with transition metal salts and inorganic oxide. The precursors may be resorcinol-formaldehyde, phenol-formaldehyde, phenolic resin, melamine-formaldehyde, polyfurfuryl alcohol, polyacrylonitrile, sucrose, polypyrrole, polydivinylbenzene and oil pitch. As salts, you can use compounds that consist of metal cations (Fe, Co, Ni, Mo, V, Y, Zr, Nb, Li, Mg, Al, Si, K, Ca, Ti, Cr, Mn, Cu, Zn , Ga, Ge, As, In, Sn, Sb, La, Hf, Ta, W) and anions (СН ₃ СОО ^- , СН ₃ СОСН = СО ^- СН ₃ , F ^- , Cl ^- , Br ^- , NO ₃ ^- , SO ₄ ^2- , PO ₄ ^3- , COO ^- , ClO ₄ ^- , RO ^- ). As oxides of inorganic materials, SiO ₂ , Al ₂ O ₃ , TiO ₂ , CeO ₂ , ZrO ₂ , SnO ₂ , Y ₂ O _{3 can be used} . The components are taken in such quantities that the precursor: salt ratio is 20: 1-1: 2, and the precursor: oxide ratio is 20: 1-1: 2.

At the second stage, a nanostructured composite is obtained, for which the initial mixture is subjected to graphitization in an inert gas atmosphere at a temperature of 300-2500 ° C for 0.1-50 hours.

In the third stage, oxides of inorganic materials are etched from the nanostructured composite. Processing can be carried out with HF, NaOH, KOH, Mg (OH) ₂ , Ca (OH) ₂ , LiOH with a concentration of 0.01-10 M at a temperature of 10-300 ° C.

At the fourth, final stage, acid treatment is carried out and a nanostructured carbon material is obtained. Processing can be carried out with HCl, HNO ₃ , H ₂ SO ₄ , HF, H ₃ PO ₄ , CH ₃ COOH with a concentration of 0.01-10 M at a temperature of 10-300 ° C.

Synthesis is given as an example, where a mixture of water, cobalt salt, nickel salt, resorcinol, formaldehyde, and quartz was mixed well, kept at 85 ° С for 3 h, and subjected to graphitization in a stream of nitrogen at 900 ° С for 3 hours. A nanostructured carbon material is obtained after mixing the composite with 3 M NaOH for 3 hours to remove quartz particles and then washing with 2.5 M HNO ₃ for 1 hour to remove metal particles.

As follows from the cited patents, the use of salts and oxides of various transition metals, including in the form of nanoparticles of these metals, can significantly reduce the graphitization temperature of the carbon material to obtain graphite nanoparticles with a large specific surface area. The presence of graphite nanoparticles is demonstrated by XRD spectra and electron microscopy photographs showing the packing of graphite packs.

The authors solve simultaneously with foaming the catalytic crystallization (graphitization) of carbon pitch in the presence of 3d metal nanoparticles (iron, cobalt, nickel) or their mixture, which is carried out at a temperature of 600-1000 ° C in an inert or exhaust gas (reducing) environment. The resulting material is penografit, from which by pressing it is possible to obtain products of the desired shape and size.

The problem is solved by the method of producing penografit by graphitization of coal tar pitch in the presence of a catalyst at a temperature of 600-1000 ° C, where nanoparticles of iron, cobalt, nickel or their mixtures deposited on a nanostructured carbon material are taken as a catalyst, and graphitization is carried out in a reducing medium, t. e. in the environment of exhaust gases, or in an inert environment. The concentration of iron, cobalt, nickel nanoparticles or a mixture thereof is 0.2-0.9% by weight of coal tar pitch and nanostructured carbon material in terms of metal. To bind benzopyrene, an additive of ferrosilicon is used in an amount of from 2 to 6% by weight of the coal tar pitch used.

The technical result is a low-temperature graphitization of a carbon material, which allows to reduce the temperature by 2–3 times and to exclude the formation and release of benzopyrene.

The inventive method is as follows.

As a catalyst, nanoparticles of 3d metals (iron, cobalt, nickel) or their mixture in the amount of 0.2-0.9 wt.% In terms of metal deposited on a nanostructured carbon material are used. The properties of the nanostructured carbon material are described in detail in the KEMERIT Trademark Certificate No. 245674. Registered in the State Register of Trademarks and Service Marks of the Russian Federation dated 05/12/2003 ”, this carbon material can be obtained from coal, coke and other carbon materials using the method described in patent RU 2206394, B01J 20/20, С01В 31 / 12, 06.20.03. To bind benzopyrene, an additive of ferrosilicon is used in an amount of from 2 to 6% by weight of the pitch used. A portion is poured into a crucible with a ground lid and placed in a muffle furnace. The furnace is heated in the selected temperature range of 600 - 1000 ° C for the set time. After the set time, the crucible is removed from the furnace and cooled in air in a desiccator at room temperature. After cooling, the crucible is weighed to calculate the carbonization constant (k = P _ref / P _carbon ).

X-ray studies were performed on diffractometer URD-6 with CuK _α radiation. The XRD spectra of the obtained samples of penografite are very similar, they consist of a graphite component with an admixture of turbostratic (defective graphite, if we use the terminology of Raman spectroscopy) carbon, the concentration ratios of which can be calculated from the ratio of the peak areas of graphite to turbostratic carbon shown in Fig. 1.

A characteristic feature of graphite is its high electrical conductivity, which is also characteristic of penografite. The temperature dependence of samples 1, 2 was measured by the four-contact method in the temperature range 300–4 K. The samples under investigation were pressed into an ampoule. The contacts to the ampoule were brought in by a silver wire with a diameter of 0.1 mm, and to make the sample contact the wire, the powder in the ampoule was pressed. Figure 2 shows the temperature dependence of the samples of penografit with the same concentration of Nickel (0) and different concentrations of ferrosilicon. Figure 2 shows that the conductivity (the reciprocal of the resistivity) of the first sample is higher than the second sample. The addition of ferrosilicon made to remove benzopyrene does not affect, and in our case it increases the conductivity of penografite, which at room temperature - 300 K corresponds to the conductivity of crystalline graphite (see Figure 3).

The temperature analysis of pyrolysis of coal tar pitch in the presence of a catalyst was carried out on a synchronous thermal analyzer STA 409 + quadrupole mass spectrometer QMS and STA 449 + quadrupole mass spectrometer QMS.

The composition of coal tar pitch includes benzopyrene, which is a condensed five-nuclear aromatic cycle that exhibits strong carcinogenic activity. For example, as noted in the book by V. A. Privalov, M. A. Stepanenko, “Coal tar pitch”, Moscow: Metallurgy, 1981, p. 38, when analyzing two samples of coal tar pitch for the content of five-membered aromatic cycles having a molecular weight of 252 g, the content of benzopyrene was 9.8 and 8.4 wt.%, and perylene - 2.3 and 1.8 wt.%, respectively.

Figure 4 shows the curve of a quadrupole mass spectrometer QMS distribution of fragments of mass 113, 126, representing the most characteristic fragments of benzopyrene, released depending on the temperature of the pyrolysis of coal tar pitch (example 8). It should be noted that the obtained results confirm the data of V.A. Privalov and M.A. Stepanenko about the presence of benzopyrene in the initial coal tar pitch, which is released during pyrolysis in the temperature range 125-350 ° С. In addition, in the process of pyrolysis of coal tar pitch at a temperature of 400-650 ° C, benzopyrene is formed. That is, as a result of pyrolysis of coal tar pitch, significantly more benzopyrene is released into the atmosphere of the reactor than it was in the initial pitch.

Figure 5 shows the characteristic curve of the QMS quadrupole mass spectrometer of the distribution of mass fragments 113, 126, representing the most characteristic benzopyrene fragments, depending on the pyrolysis temperature of the pitch in the presence of a sample of the catalyst (cobalt nanoparticles). It should be noted that in figure 2, in the temperature range 125-250 ° C, benzopyrene, which is present in the pitch, is released, and benzopyrene, which is formed during the further pyrolysis of the pitch, is absent. A similar picture is observed when using nickel and iron nanoparticles (examples 1, 3, 4, 5).

This suggests that 3d metal nanoparticles during the pyrolysis of coal tar pitch prevent the formation of benzopyrene during the catalytic synthesis of penografite from coal tar pitch, but do not bind the benzopyrene that was present in the pitch.

Figure 6 shows a curve of a QMS quadrupole mass spectrometer for the distribution of mass fragments 113, 126, representing the most characteristic benzopyrene fragments, depending on the temperature of the pyrolysis of coal tar pitch in the presence of a ferrosilicon suspension (manufactured by the Novokuznetsk ferroalloy plant) used as a catalyst (example 9) . It should be noted that in this case there are no traces of benzopyrene in the temperature range 125-350 ° C, but appear in the temperature range 400-600 ° C, when the bulk of the pitch is subjected to pyrolysis.

As the authors noted earlier (above), 3d-metal nanoparticles completely suppress the formation of benzopyrene during the pyrolysis of coal tar pitch, and ferrosilicon binds benzopyrene, which is present in the pitch at the initial stage of pyrolysis. When using a mixture of 3d metal nanoparticles and ferrosilicon, the release of benzopyrene during the pyrolysis of coal tar pitch is completely suppressed. Figure 7 shows the TG, DSC curve of the STA 449 thermal analyzer (examples 2.10), which shows that the pyrolysis of the pitch is taking place, and the emission or formation of fragments of masses 113, 126 representing benzopyrene is not recorded on the curve of the QMS quadrupole mass spectrometer .

The data presented suggest that the use of a mixture of 3d metal nanoparticles and ferrosilicon completely suppresses the release of benzopyrene into the atmosphere of the reactor on the one hand and, on the other hand, increases the carbon residue yield not only due to the bound benzopyrene, but also the binding of other volatile carbon components of the pitch.

The invention is illustrated by the following examples.

Example 1

A sample of medium-temperature pitch of Altai Koks OJSC 5.0030 g is mixed with a Kemerit sample 0.5964 g containing nickel nanoparticles (0) 0.0288 g, placed in a crucible with a ground lid, which is then placed in a standard muffle furnace. The temperature in the furnace is gradually raised to 900 ° C and maintained at this temperature for 10 minutes. After that, the crucible is transferred from the furnace to a desiccator and cooled in air to room temperature. The output of penografit 0.52. The ratio of the concentration of the peak areas of graphite to turbostratic carbon is 0.71.

Example 2

A sample of medium-temperature pitch of Altai Koks OJSC 5.0386 g is mixed with a Kemerit sample of 0.6216 g containing nickel nanoparticles (0) 0.0301 g and 0.6176 g of ferrosilicon, placed in a crucible with a ground lid, which is then placed in a standard muffle furnace. The temperature in the furnace is gradually raised to 900 ° C and maintained at this temperature for 10 minutes. After that, the crucible is transferred from the furnace to a desiccator and cooled in air to room temperature. The output of penografit 0.58. The ratio of the concentration of the peak areas of graphite to turbostratic carbon is 0.65.

Example 3

A portion of the high-temperature pitch of Kemerovo Coke OJSC 5.0330 g is mixed with a Kemerita portion 0.6064 g containing nickel nanoparticles (0) 0.0278 g, placed in a crucible with a ground lid, which is then placed in a standard muffle furnace. The crucible was gradually heated to 600 ° C and held for 320 minutes. After that, the crucible is transferred from the furnace to a desiccator and cooled in air to room temperature. The output of penografit 0.62. The ratio of the concentration of the areas of the graphite peaks to turbostratic carbon is 1.5.

Example 4

A portion of the high-temperature pitch of OJSC Kemerovo Coke 5.0130 g is mixed with a portion of Kemerite 0.6004 g containing cobalt nanoparticles (0) 0.0268 g, placed in a crucible with a ground lid, which is then placed in a standard muffle furnace. The temperature in the furnace is gradually raised to 900 ° C and maintained at this temperature for 10 minutes. After that, the crucible is transferred from the furnace to a desiccator and cooled in air to room temperature. The output of penografit 0.55. The ratio of the concentration of the peak areas of graphite to turbostratic carbon is 0.78.

Example 5

A sample of medium-temperature pitch of Altai Koks OJSC 5.0030 g is mixed with 0.5969 g of Kemerit sample containing iron nanoparticles (0) of 0.0288 g, placed in a crucible with a ground lid, which is then placed in a standard muffle furnace. The temperature in the furnace is gradually raised to 900 ° C and maintained at this temperature for 10 minutes. After that, the crucible is transferred from the furnace to a desiccator and cooled in air to room temperature. The output of penografit 0.53. The ratio of the concentration of the peak areas of graphite to turbostratic carbon is 0.71.

Example 6

A portion of the high-temperature pitch of Kemerovo Coke OJSC 5.0230 g is mixed with a Kemerita sample of 0.3004 g containing nickel nanoparticles (0) 0.0140 g and 0.3035 g of coke containing iron nanoparticles 0.0146 (0) g in a crucible with a ground lid, which is then placed in a standard muffle furnace. The temperature in the furnace is gradually raised to 600 ° C and maintained at this temperature for 180 minutes. After that, the crucible is transferred from the furnace to a desiccator and cooled in air to room temperature. The output of penografit 0.62. The ratio of the concentration of the areas of the graphite peaks to turbostratic carbon is 1.19.

Example 7

A portion of the medium-temperature pitch of Altai Koks OJSC 5.0130 g is mixed with a Kemerite sample 0.3010 g containing iron nanoparticles (0) 0.0140 g and 0.3015 coke containing 0.0140 nickel nanoparticles (0) are placed in a crucible with a ground lid, which is then placed in a standard muffle furnace. The temperature in the furnace is gradually raised to 600 ° C and maintained at this temperature for 10 minutes. After that, the crucible is transferred from the furnace to a desiccator and cooled in air to room temperature. The output of penografit 0.52. The ratio of the concentration of the areas of graphite peaks to turbostratic carbon is 2.24.

Example 8

For temperature analysis of pyrolysis of coal tar pitch, a sample of medium-temperature pitch in the amount of 30-40 mg is taken and carried out on a STA 409 + synchronous thermal analyzer of a quadrupole mass spectrometer. Helium is used as an inert gas. The rate of temperature rise is 10 ° C / min from room temperature to 1000 ° C. The yield of coke residue is 0.57. The ratio of the concentration of the peak areas of graphite to turbostratic carbon is 0.58. The curve of the QMS quadrupole mass spectrometer of the distribution of mass fragments 113, 126, representing the most characteristic fragments of benzopyrene, released depending on the temperature of the pyrolysis of coal tar pitch, is presented in Figure 4.

Example 9

A portion of the high-temperature pitch of OJSC Kemerovo Coke 5.0386 g is mixed with a portion of 0.6176 g of ferrosilicon. Part of the mixture (40 mg) was taken for analysis on a synchronous thermal analyzer STA 409 + quadrupole mass spectrometer. Helium is used as an inert gas. The rate of temperature rise is 10 ° C / min from room temperature to 1000 ° C. The yield of coke residue is 0.60. The ratio of the concentration of the areas of the graphite peaks to the turbostratic carbon is 0.60. The curve of the QMS quadrupole mass spectrometer of the distribution of mass fragments 113, 126, representing the most characteristic benzopyrene fragments, released depending on the pyrolysis temperature of coal tar pitch, is presented in FIG. 5.

Example 10

A portion of the high-temperature pitch of Kemerovo Coke OJSC, 5.0386 g, is mixed with a 0.6216 g Kemerite sample containing iron nanoparticles (0) 0.0288 g and 0.6176 g ferrosilicon, placed in a crucible with a ground cap, which is then placed in a standard muffle furnace. The temperature in the furnace is gradually raised to 900 ° C and maintained at this temperature for 10 minutes. After that, the crucible is transferred from the furnace to a desiccator and cooled in air to room temperature. The output of penografit 0.58.

A part of this mixture (35 mg) was taken for analysis on a STA 409 synchronous thermal analyzer with a quadrupole mass spectrometer. The curves of the quadrupole mass spectrometer of the distribution of mass fragments with m / z 113, 126, representing the most characteristic fragments of benzopyrene, released depending on the pyrolysis temperature of coal tar pitch, are presented in Fig.7.

The proposed method allows to carry out low-temperature graphitization of the carbon material and to exclude the formation and allocation of benzopyrene.

Claims (3)

1. A method of producing penografit by graphitization of coal tar pitch in the presence of a catalyst at a temperature of 600-1000 ° C, where nanoparticles of iron, cobalt, nickel or mixtures thereof deposited on a nanostructured carbon material are taken as a catalyst, and graphitization is carried out in a reducing medium, t. e. in the environment of exhaust gases, or in an inert environment. 2. The method according to claim 1, characterized in that the concentration of iron, cobalt, nickel nanoparticles or a mixture thereof is 0.2-0.9% by weight of coal tar pitch and nanostructured carbon material in terms of metal. 3. The method according to claim 1, characterized in that for the binding of benzopyrene use an additive of ferrosilicon in an amount of from 2 to 6% by weight of the used coal tar pitch.

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