RU2310601C2 - Method of production of the carbonic nanotubes with the incapculated particles of nickel and cobalt and the installation for the synthesis of the materials based on the carbonic nanotubes and nanoparticles of nickel and cobalt - Google Patents

Abstract

FIELD: chemical industry; methods and the devices for manufacture of the catalysts, the stationary chromatographic phases, the materials for sorption of the hydrogen.

SUBSTANCE: the invention may be used at manufacture of the catalysts, the stationary chromatographic phases, the materials for sorption of the hydrogen. The invention provides, that prepare the solution of acetylacetonate of the cobalt or of the nickel in benzol or its mixture with the alcohol. The vessel (11) is filled with the produced solution. Fill the bubbler (3) with benzol. The installation is sealed and filled with the nitrogen from the balloon (8). The quartz reactor (1) made with the capability of heating in the high-temperaturefurnace (5)is heated up in the nitrogen flow fed from the balloon (8). Then the nitrogen from the balloon (9) is fed into the vessel (11) under pressure and they sputter the solution of the cobalt or nickel acetylacetonate through the capillary tube (2) in the reaction zone of the reactor (1) with production of the corresponding catalyst. After that they feed benzol from the bubbler (3) into the reactor (1). As a result of it the decomposition of the benzol on the catalyst takes place. The invention allows to simplify the production process, to reduce the power inputs, to increase the yield and the quality of the carbonic nanotubes with the incapsulated particles of the nickel and cobalt.

EFFECT: the invention ensures simplification of the production process, reduction of the power inputs, the increase of the yield and the quality of the carbonic nanotubes with the incapsulated particles of the nickel and cobalt.

2 cl, 15 dwg

Description

The invention relates to the field of chemical technology for the production of composite carbon-metal materials, and in particular to a method for producing carbon nanotubes containing nanoscale particles of cobalt and nickel metals. The invention relates to a catalytic method for the production of carbon nanotubes from hydrocarbons. It can be used in the production of sorbents, catalysts, stationary chromatographic phases, materials for hydrogen sorption. Such properties of composite materials based on carbon nanotubes, such as mechanical elasticity and noticeable electrical conductivity, suggest the use of such materials in the electronics industry.

The choice of nickel and cobalt metals for the synthesis of composite materials based on carbon nanotubes (CNTs) is due to the possibility of application in catalysis, hydrogen energy, and the creation of magnetic and radar absorbing coatings, as well as the fact that these metals are the most effective catalysts for the growth of CNTs (they exhibit catalytic activity upon decomposition of volatile carbon-containing compounds, they form metastable carbides, carbon is able to diffuse fairly quickly in these metals).

A known catalytic method for producing CNTs is based on chemical gas-phase deposition of carbon during the decomposition of acetylene on cobalt particles at 700 ° C (M. Jose-Yacaman, L. Rendon at al., Appl. Phys. Lett. 62 (1993) 657). According to the known method, 2.5 wt.% Fe is used as a catalyst on graphite, reduced at a temperature of 350 ° C, to decompose a mixture of 9% acetylene in nitrogen at 700 ° C. The total amount of carbon formed was not measured, it is only reported that 65% of graphite tubular carbon fibers are formed. The diameter of the tubes is from 5 to 50 nm and the length is up to 50 mm, while the diameters of the tubes are controlled by the size of the iron particles, and the length by the reaction time.

In the work of K. Hernady, A.Fonseca, J.B. Nagy at al., Carbon 34 (10) (1996) 1249 also used 2.5 wt.% Fe on a support as a catalyst, but silica gel was chosen as a support. The decomposition of acetylene, as well as ethylene, propylene and methane at a temperature of 650-800 ° C, was studied on this catalyst. It was shown that the highest yield of CNTs is obtained upon decomposition of acetylene at 700 ° С. The resulting CNTs with a maximum yield of 184% have average diameters of 20 nm. Under accepted conditions, methane does not decompose and does not form nanotubes.

In the work of W. Li, S. Xie, J. Wang; Science 274 (1996) 1701 to obtain direct CNTs, iron nanoparticles embedded in the pores of mesoporous silica gel are used as a substrate for the decomposition of a mixture of 9% acetylene in nitrogen. The decomposition of acetylene is also carried out at 700 ° C. In 2 hours, a film with a thickness of about 50 mm grows, consisting of many carbon nanotubes with average diameters of about 30 nm and channels of 4 nm.

A widespread method for producing CNTs at high temperature decomposition of methane [A. Oberlin, M. Endo, T. Koyama, J. Cryst. Growth 32 (1976) 335, G. Tibbetts, M. Devour, E. Rodda; Carbon 25 (1987) 367, F. Benissad, P. Gadelle at al .; Carbon 26 (1988) 61]. Methane mixed with hydrogen decomposes when a suspension of dispersed iron particles (about 12 nm in size) is fed to the reactor at a temperature above 1000 ° C. In a few seconds, long carbon filaments are formed, which are not nanotubes, but pyrolytic carbon.

There is also known a method by which CNTs in large quantities are obtained by decomposition of acetylene in a fixed layer of an supported iron catalyst at a temperature of 700 ° C. The catalyst contains 2.5 wt.% Metallic iron on a substrate of graphite, zeolite or silica gel. CNTs are formed as a result of growth on iron crystallites that make up the catalyst [K. Hemady, A. Fonseca, J.B. Nagy at al., Carbon 34 (10) (1996) 1249]. The main disadvantages of the described method for producing carbon nanotubes are as follows.

1. The specificity of the proposed catalyst for producing carbon nanotubes. In the prototype, nanotubes are obtained only by the decomposition of acetylene. Ethylene produces three times less carbon nanotubes. Methane does not decompose under accepted conditions even at 800 ° C.

2. Low yield of CNTs per unit catalyst mass during the period of its deactivation (184% of carbon deposits are formed). The low carbon yield may be due to the low content of active metal in the catalyst, as well as its rapid deactivation due to the deposition of amorphous carbon on the surface of the tubes, which the authors themselves note. The latter can be caused by uneven compaction of carbon in the fixed catalyst bed and possible temperature variability throughout the catalyst bed.

3. The difficulty in separating carbon nanotubes due to the large amount of carrier phase in a carbonized catalyst.

A known method of producing CNTs by decomposing a hydrocarbon on an iron-containing catalyst at elevated temperature, characterized in that for the production of carbon nanotubes, methane decomposition is carried out in a vibro-fluidized catalyst layer at a temperature not exceeding 650 ° C in the presence of a catalyst containing iron, cobalt and alumina in the following ratio , wt.%: iron - 25-85. cobalt - 5-75, aluminum oxide - the rest (RU No. 2146648, СВВ 31/02, В82В 3/00, publ. 2000.03.20).

According to the known method, 0.2 g of a granular catalyst in a reduced state with a particle size of 0.25-0.50 mm is poured into a reactor with a diameter of 30 mm, containing, wt.%: Iron - 85, cobalt - 5 and aluminum oxide - 10. Catalyst contains iron and cobalt in the form of crystallites of iron-cobalt alloy with a size of about 30 nm. Using a vibrodrive, the catalyst is vibro-fluidized, heating is turned on and the temperature of the catalyst layer is adjusted to 625 ° C. Then methane is fed to the catalyst, which, passing through the catalyst bed, decomposes into carbon and hydrogen. Hydrogen and unreacted methane are removed from the reactor. The methane flow rate is maintained so that the contact time of the reactant and catalyst is 0.06 sec. The carbon formed remains on the catalyst and is completely retained in the reactor. The process is conducted for 17 hours until the catalyst is completely deactivated. The carbon from the catalyst is separated by dissolving the catalyst in dilute hydrochloric acid.

This decision was made as a prototype for the claimed method.

The known method allows to obtain CNTs with high yield and ensures the purity and uniformity of the resulting nanotubes. Moreover, the obtained, mainly direct, CNTs do not contain amorphous carbon on their surface. In addition, as a result of the catalytic decomposition of methane, in addition to CNTs, hydrogen is formed in parallel.

However, this known method has the disadvantage of complexity of execution.

A known installation for the synthesis of materials based on carbon nanotubes and nickel or cobalt nanoparticles, containing a quartz reactor made with the possibility of heating in a high-temperature furnace, gas cylinders and a unit for measuring and controlling the heating temperature of the quartz reactor having thermocouples for measuring the temperature outside and inside the quartz reactor (RU No. 2108966, СВВ 31/00, СВВ 31/02. publ. 1998.04.20).

This decision was made as a prototype for the claimed device.

A disadvantage of the known installation for synthesis is that it is designed exclusively for the use of non-deficient sources of carbon raw materials - propane and propane-propylene fraction, without taking into account that the choice of starting material should be determined by the result that should be obtained at the output of the reaction.

The present invention solves the problem of developing a method for producing CNTs, which provides a high yield of CNTs per unit mass of catalyst while ensuring the purity and uniformity of the obtained CNTs.

The technical result achieved in this case is to simplify the process, reduce energy consumption, increase the yield and quality of oriented CNTs filled with metal obtained by this method.

The specified technical result for the method is achieved in that in the method for producing carbon nanotubes with encapsulated particles of nickel and cobalt, which consists in the fact that when the hydrocarbon is decomposed into a cobal- or nickel-containing catalyst at an elevated temperature, the cobal- or nickel-containing catalyst (cobalt and nickel acetylacetonates) fed to the reaction zone in the form of a solution in organic liquids sprayed directly in the reaction zone, while organic solvent is used as a solvent the temperature in which cobalt and nickel acetylacetonates are soluble.

The specified technical result for the device is achieved in that the installation for the synthesis of materials based on carbon nanotubes and nickel or cobalt nanoparticles, containing a quartz reactor configured to heat it in a high-temperature furnace, gas cylinders and a unit for measuring and controlling the heating temperature of the quartz reactor, having thermocouples for measuring the temperature outside and inside the quartz reactor are equipped with a capillary communicated on the one hand with the internal cavity of the quartz reactor, and on the other hand with one of the cylinders with nitrogen and filled with metal acetylacetonate, a bubbler filled with benzene, through which a stream of pure hydrogen enters the quartz reactor, controlled by a valve built into the communication channel of the bubbler with a quartz generator to communicate with the cavity of the last second nitrogen tank.

These features are essential with the formation of a stable set of essential features sufficient to obtain the desired technical result.

The present invention is illustrated by a specific example, which clearly demonstrates the possibility of achieving the above set of features of the desired technical result.

Figure 1 - installation for the synthesis of systems based on CNTs and nanoparticles of nickel and cobalt;

figure 2 is a micrograph of a sample obtained by thermal decomposition of vapors of benzene and nickel acetylacetonate, a scale scale of 2 μm;

figure 3 is the same as in figure 2, the scale scale is 200 nm;

4 is a micrograph of a sample obtained by injection of a 0.5% solution of nickel acetylacetonate into the high temperature region, a scale scale of 5 μm;

figure 5 is the same as in figure 4, a scale scale of 2 μm;

6 is a micrograph of a CNT sample obtained by direct injection of a 0.5% solution of nickel acetylacetonate in a mixture consisting of benzene (40%) and ethanol (60%) into the reaction zone at a temperature of 980-1070 ° C, the scale scale is 10 microns;

Fig.7 is the same as in Fig.6, the scale scale is 200 nm;

Fig. 8 is a photomicrograph of a CNT sample obtained by direct injection of a 1.0% solution of nickel acetylacetonate in a mixture consisting of benzene (40%) and ethanol (60%) into the reaction zone at a temperature of 980-1070 ° C; scale scale is 5 microns;

Fig.9 is the same as in Fig.7, the scale scale is 200 nm;

figure 10 is a micrograph of a sample of CNTs obtained by direct injection of a 1.5% solution of nickel acetylacetonate in a mixture consisting of benzene (40%) and ethanol (60%) into the reaction zone at a temperature of 980-1070 ° C. scale scale - 5 microns;

11 - the same as in figure 10, the scale scale is 300 nm;

12 is a photomicrograph of a CNT sample obtained by direct injection of a 1.0% solution of nickel acetylacetonate in a mixture consisting of benzene (40%) and ethanol (60%) into the reaction zone at a temperature of 980-1070 ° C, a scale scale of 500 nm;

Fig.13 is the same as in Fig.12, the scale scale is 100 nm;

Fig - micrograph of a CNT sample obtained by direct injection of a solution of nickel acetylacetonate in a mixture consisting of benzene (40%) and ethanol (60%) into the reaction zone at a temperature of 980-1070 ° C, the concentration of the initial solution is 0.5%, scale scale of 1 micron;

Fig - micrograph of a CNT sample obtained by direct injection of a solution of nickel acetylacetonate in a mixture consisting of benzene (40%) and ethanol (60%) into the reaction zone at a temperature of 980-1070 ° C, the concentration of the initial solution is 1.0%, scale scale of 50 nm.

The following commercially available preparations were used as starting materials for the synthesis of samples in systems based on CNTs and nickel and cobalt nanoparticles: benzene (> 99.9%, Merck), cobalt (II) acetylacetonate (> 98%, Merck), nickel acetylacetonate (II) (> 98%, Merck), ethyl alcohol (spectrally pure, Merck), deionized water (6 MΩ).

According to the present invention, a method for producing CNTs with encapsulated nickel and cobalt particles is that when the hydrocarbon is decomposed into a cobalt or nickel-containing catalyst at an elevated temperature, the cobalt or nickel-containing catalyst (cobalt and nickel acetylacetonates) is fed into the reaction zone as a solution in organic liquids sprayed with high pressure directly in the reaction zone, while a volatile organic liquid in which we are cobalt and nickel acetylacetonates.

Synthesis using nickel (II) and cobalt (II) acetylacetonates was carried out using the apparatus shown in Fig. 1. The main components of the installation are a quartz reactor 1, in which the synthesis of nanocomposites takes place, a capillary 2 with an internal diameter of 70 μm and an external diameter of 100 μm, a bubbler 3 containing benzene, through which a stream of highly pure hydrogen from the GHF-12 generator is blown, temperature control 4, responsible for heating the reactor 1, a high-temperature tube furnace 5, a controlling thermocouple 6, located outside the reactor, a measuring thermocouple 7, located in a quartz pocket directly in the reaction zone, cylinder 8 and 9 with N _2, as well as valves 10 and the system gas flow regulators for controlling the filling gas system. A solution of metal acetylacetonate is supplied through capillary 2 from the vessel 11. The temperature measurement and control unit is a conditional concept providing understanding of the modularity of the installation. In fact, these are thermocouples and a controller that provides signal registration from them.

For the experiment, 25 ml of solutions of nickel and cobalt acetylacetonates with mass concentrations of 0.5, 1, and 1.5% were preliminarily prepared. For this, the calculated sample of nickel or cobalt acetylacetonate was dispersed in 25 ml of benzene or in 25 ml of a mixture consisting of 10 ml of benzene and 15 ml of ethyl alcohol. To accelerate the dissolution process, the resulting suspension was sonicated for 15 minutes, and a true solution was formed. The vessel 11 was filled with 25 ml of the resulting solution, the bubbler 3 was filled with 60 ml of benzene, then the installation was sealed, for this connection the sections were lubricated with concentrated phosphoric acid, densely ground and filled with nitrogen from cylinder 8. The reactor 1 was heated to a temperature of 1000 ° C for 2 hours in a stream of nitrogen with a space velocity of 800 ml / min. After the temperature in reactor 1 was established, a stream of hydrogen was passed through the system at a space velocity of 100 ml / min. After checking the purity of hydrogen, nitrogen was supplied to vessel 11 from cylinder 9 under a pressure of 6 atm. In this case, a solution of the metal acetylacetonate was sprayed through capillary 2 in the reaction zone. Spraying continued for 3 minutes, the flow rate was about 7-9 ml / min, after which saturated benzene vapor in hydrogen was passed through the system for 30 minutes. Next, the system was filled with nitrogen and cooled to room temperature for 4-5 hours. Samples were collected from the walls of the reactor and from the surface of the “pocket” of the thermocouple from various temperature zones.

The samples were studied by scanning electron microscopy on a LEO 1440VP instrument, transmission electron microscopy (LEO 912 AB), as well as X-ray microanalysis (JEOL JSM-840 + LINK AN-10000 (20 kV, 120 s, ZAF), thermogravimetric analysis (NETZSCH STA 409PC), Raman spectroscopy (Dilor Z-24, Ar - 5 mW laser).

We have proposed a fundamentally new approach to the synthesis of systems based on CNTs and metal nanoparticles. The fundamental difference is that organometallic precursors are not supplied to the reaction zone in a gaseous form, but in the form of a solution in organic liquids sprayed directly in the reaction zone. According to our assumption, such a feed of an organometallic precursor allows one to create conditions that differ greatly from equilibrium. The solvent can presumably be any organic liquid in which cobalt and nickel acetylacetonates are soluble. The optimal concentration of nickel and cobalt acetylacetonate was, according to our calculations, 0.5% wt.

Obtaining samples containing CNTs has confirmed the possibility of using our synthesis method. To further develop this method, we studied the dependence of the quality of the obtained nanotubes on the concentration of nickel acetylacetonate in the initial solution. For these purposes, we conducted experiments with stock solutions of various concentrations: 0.5, 1.0, 1.5%. 6, 7 are microphotographs of CNT samples obtained by direct injection of a 0.5% solution of nickel acetylacetonate in a mixture consisting of benzene (40%) and ethanol (60%) into the reaction zone at a temperature of 980-1070 ° C, scale of 10 microns and 200 nm). With an increase in the solution concentration to 1.0 wt%, multilayer CNTs also formed, but their morphology differed from the samples obtained using a 0.5% solution (Figs. 8, 9 are micrographs of CNT samples obtained by direct injection of a 1.0% solution Nickel acetylacetonate in a mixture consisting of benzene (40%) and ethanol (60%), into the reaction zone at a temperature of 980-1070 ° C, a scale scale of 5 μm and 200 nm). Nanotubes with a diameter of 30-50 nm a few microns in length were folded into spherical balls of a diameter of about 5 microns. In this case, no formation of amorphous carbon particles was observed. At the ends and cavities of the CNT, metal particles about 40 nm in size are clearly visible. No metal outside the CNT cavities was observed.

With a further increase in the concentration of nickel acetylacetonate in the initial solution, there is a certain excess of metal particles in the reaction zone. As a result of this, the nanoparticles agglomerate into larger phases in which nanotube growth does not occur. In microphotographs (Fig. 10, 11 are microphotographs of CNT samples obtained by direct injection of a 1.5% solution of nickel acetylacetonate in a mixture consisting of benzene (40%) and ethanol (60%) into the reaction zone at a temperature of 980-1070 ° C , a scale scale of 5 μm and 300 nm) of samples obtained using 1.5% solutions of acetylacetonates, nickel particles larger than 100 nm are visible. The formation of a small amount of carbon fibers with a diameter of 150-200 nm was also observed.

Typical images obtained by transmission electron microscopy are shown in Figs. 12, 13 — micrographs of CNT samples obtained by direct injection of a 1.0% solution of nickel acetylacetonate in a mixture consisting of benzene (40%) and ethanol (60%) into the reaction zone at a temperature of 980-1070 ° C, a scale scale of 500 nm and 100 nm. The outer diameter of the nanotubes was 60 ± 5 nm. It is also clearly seen that the nanotubes are more defective than in the case of using dicyclopentadienyl iron, amorphous carbon particles are observed on the outer surface.

Synthesis using cobalt acetylacetonate.

When using cobalt acetylacetonate as an organometallic precursor, we observed almost the same dependence of the obtained samples on the concentration of the initial solution. The only difference was the absence of harnesses when using a 0.5 wt.% Solution (Fig. 14). In the case of the use of initial solutions with concentrations of 1.0 and 1.5% in electron micrographs, CNTs were observed, similar to the case of nickel acetylacetonate. According to transmission electron microscopy, the outer diameter of the nanotubes was calculated; it amounted to 60 ± 5 nm. When using a 1.5% solution, the formation of a large number of cobalt particles of different sizes, reaching hundreds of nm, was also observed.

In the apparatus depicted in FIG. 1, pivalates of these metals, as well as binuclear pivalate cluster complexes of nickel and cobalt — Co ₂ (c-H ₂ O) (c-OOCCMez) 2 (precursors of cobalt and nickel-containing catalysts) can be used OOSSMez) 2 (NOOSSMez) ₄ and Ni ₂ (p-H ₂ O) (p-OOSSMez) 2 (OOSSMez) 2 (NOOSSMez) _4. The method of the experiment, including the concentration of the reagents and the volumes of the solutions, remains the same.

For the experiment, 25 ml of solutions of nickel and cobalt pivalates with mass concentrations of 0.5, 1, and 1.5% were ultrasonically dispersed in 25 ml of benzene or in 25 ml of a mixture consisting of 10 ml of benzene and 15 ml of ethyl alcohol. The vessel 11 was filled with 25 ml of the resulting solution, the bubbler 3 was filled with 60 ml of benzene, then the installation was sealed, for this connection the sections were lubricated with concentrated phosphoric acid, rubbed tightly and filled with nitrogen from a cylinder & JReaKTop 1 was heated to a temperature of 1000 ° C for 2 hours in a stream of nitrogen with a space velocity of 800 ml / min. After the temperature in reactor 1 was established, a stream of hydrogen was passed through the system at a space velocity of 100 ml / min. After checking the purity of hydrogen, nitrogen was supplied to vessel 11 from cylinder 9 under a pressure of 6 atm. In this case, a solution of the metal acetylacetonate was sprayed through capillary 2 in the reaction zone. Spraying continued for 3 minutes, the flow rate was about 7-9 ml / min, after which saturated benzene vapor in hydrogen was passed through the system for 30 minutes. Next, the system was filled with nitrogen and cooled to room temperature for 4-5 hours.

General to all examples: the temperature of the reactor can vary in the range of 650-1150 ° C.

Output.

1. For the first time, a method for the synthesis of carbon nanotubes with encapsulated particles of nickel and cobalt by injection of solutions of their complexes in ethanol and benzene was implemented.

2. The presence of ethanol has a significant effect on the morphology of the resulting composites: the formation of oriented nanotubes is observed.

The present invention is industrially applicable, as it is implemented using known components, and the result is achieved due to new conditions for the synthesis.

Claims (2)

1. A method of producing carbon nanotubes with encapsulated transition metal particles, comprising decomposing a hydrocarbon at an elevated temperature on a catalyst containing a transition metal, characterized in that a solution of cobalt or nickel acetylacetonate in benzene or its mixture with ethyl alcohol is sprayed directly in the reaction zone with the receipt of the corresponding catalyst, and benzene is used as the hydrocarbon. 2. Installation for the synthesis of materials based on carbon nanotubes with encapsulated particles of nickel or cobalt, containing a quartz reactor made with the possibility of heating in a high-temperature furnace, and means for supplying gases, characterized in that it is additionally equipped with a capillary injector communicated, on the one hand , with a reactor, and on the other, with a cylinder for supplying nitrogen through a vessel filled with nickel or cobalt acetylacetonate, a bubbler for feeding benzene with pure hydrogen into the reactor, a valve built into communication with a quartz bubbler generator and a second nitrogen supply cylinder, as well as thermocouples for measuring the temperature outside and inside the reactor.

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