RU2296708C1 - Method of manufacture of the composite material made on the basis of the expanded graphite - Google Patents

Abstract

FIELD: chemical industry; methods of manufacture of the composite materials on the basis of the expanded graphite.

SUBSTANCE: the invention may be used at manufacture of the adsorbents, the porous carbon carriers and the metal=containing catalytic agents. The method provides, that first prepare the 1-2 % cellulose solution in the 5-8.5 % sodium hydroxide water solution. The produced solution is mixed with the expanded graphite in the mass ratio of the graphite to the cellulose of (1-2.5) : (2-1) accordingly. The composition prepared this way is carbonize with heating rate of 4°C per a minute up to 600°C maintaining this temperature within 1 hour. To impart the composite material the catalytic and adsorption properties the cellulose solution may be added with 2-5 mass % of the modifying compound of the transition metal in terms of the metal. The invention ensures simplification of the composite material production process, the improvement of its quality due to the homogeneity of allocation of the active carbon in the lower die of the expanded graphite.

EFFECT: the invention ensures simplification of the composite material production process, the improvement of its quality.

2 cl, 2 tbl, 10 ex

Description

The invention relates to the production of composite carbon materials from thermally expanded natural graphites and cellulosic materials, which can be used as adsorbents, porous carbon supports and metal-containing catalysts based on them.

Various methods are known for producing composite materials based on cellulose derivatives and expanded graphite. Expanded graphites are an excellent filler for the preparation of composite carbon materials. The use of viscous solutions of metal-containing cellulosic materials as binders for compositions based on expanded graphites opens the way for the production of porous fibrous carbon carriers and catalysts.

Known methods (US 6689295, 02/10/2004; US 6024900, 02.15.2000; US 4777083, 10/11/1988) for producing composite materials based on expanded graphites, where thermoplastic reagents (polyfurfuryl alcohol are used as binders that serve as an additional source of active carbon) , phenolaldehyde polymers, etc.).

The disadvantages of the above methods is the use of heat-shrink binders and sealants, representing explosion and fire hazard, toxicity due to the use of volatile substances for the preparation of solutions. In addition, the long stages of preparation of the binder, impregnation of the components, drying of the solvent, activation, etc. limit the production and economic benefits of the process. The disadvantages include and, as a rule, the necessary additional stage of activation, because during the initial heat treatment, blocking of the pores of the carbon material is observed, which makes the process longer and energy-intensive.

It is known to obtain porous composite materials based on cellulose or its derivatives (RU 2134701, 08.20.1999; RU 2109767, 04.04.1998) using graphite as a filler and a thermoplastic polymer as a binder. In the resulting compositions, both the fibrous material and the inorganic aggregate are uniformly dispersed throughout the bulk of the molding material. After pressing the mass under pressure, drying by heating and heat treatment of the molded material at the melt temperature of the thermoplastic polymer, porous composite materials of general purpose, resistant to abrasion, with a pore structure providing the purification of gases and liquids, are obtained.

However, these methods suggest a long stage of grinding the original cellulosic materials into microfiber pulp. Continuous extreme grinding of the starting components makes it necessary to use special technological equipment and devices, such as fiber mills, refiners, defibrillation devices, as well as a number of auxiliary tools for carrying out the process. All this requires high energy costs and, to a large extent, leads to an increase in the cost of the final product.

The closest in technical essence and purpose is a method for producing a composite material based on expanded graphite and active carbon (US 6790390, 09/14/2004). The specified composite is obtained by heat treatment (350-900 ° C) with a heating rate of 4 ° C / min of a mixture of expanded graphite, an activating agent and an active carbon precursor at a temperature and time sufficient to provide a carbon precursor loss rate between 5 and 70 masses. % Cellulosic materials (wood, nutshells) or high carbon resins are a precursor to active carbon. Activating agents are chemicals (potassium hydroxide, phosphoric acid, Lewis acids), used both in pure form and in the form of concentrated solutions or melts.

The disadvantages of this method are multi-stage and the duration of the preparation of the composition in the initial stages. So, the source cellulosic material is pulverized into a dusty powder and mixed with an activating chemical agent at a temperature of 80 ° C for 21 hours, which requires a large expenditure of energy. In addition, the mechanical mixing of components with expanded graphite does not fully provide a homogeneous homogeneous mixture due to insufficient contact between them. The prolonged curing of the composite block at the final stage of heat treatment for 5 hours, together with the above disadvantages, makes the implementation of the technical task difficult from a technological and economic point of view.

The objective of the invention is:

- Simplification of the technology for producing composite material

- Improving the quality of the composite material by ensuring a uniform distribution of active carbon in the expanded graphite matrix

- Giving the composite material catalytic and adsorption properties through the introduction of modifying metal compounds

The problem is solved in that in the method for producing a composite material, comprising preparing a composition consisting of expanded graphite, cellulose and an aqueous solution of an activating agent, and its subsequent carbonization with a heating rate of 4 ° C / min to 600 ° C, according to the invention, first 1 A -2% solution of cellulose in an activating agent, which is used as a 5-8.5% sodium hydroxide solution, to prepare the composition, the resulting solution is mixed with expanded graphite in a mass ratio of 1-2.5: 2-1, respectively That is, carbonization is carried out by keeping the obtained composition at the above temperature for 1 hour. In addition, 2-5% of the transition metal modifying compound in terms of metal is added to the cellulose solution to impart catalytic and adsorption properties to the composite material.

Comparative analysis with the prototype shows that, unlike the prototype, the claimed invention preliminarily prepares a solution of cellulose in an aqueous alkali solution. The use of cellulosic material and an activating agent in the composition in the form of a solution can significantly reduce the stage of mixing the cellulosic material and activating agent (from 21 hours to 1 hour). Due to this distinguishing feature, it was possible to increase the contact efficiency of the components of the composition without additional use of a binder and to achieve uniform distribution of active carbon in the expanded graphite matrix, which contributes to the uniform development of the porous structure in the composite material.

In addition, a distinctive feature of the prototype is the addition of transition metal compounds to the cellulose solution, which allows the composite carbon material to inform the catalytic and adsorption properties, as well as to reduce the duration of the carbonization process.

The acceleration of the carbonization process from 5 hours to 1 hour is observed as a result of various factors: due to the good thermal conductivity of expanded graphite, the uniform distribution of the components of the composition over the entire volume of the sample, and the catalytic effect of the introduced activating metal additives.

The introduction into the alkaline cellulose solution of an aqueous solution of transition metal compounds (Ni, Cu, Pd) leads to the fact that the associates of solvated cellulose macromolecules are in close contact with the introduced complexes. The interaction is mainly carried out due to hydrogen bonds formed between the hydroxyls of alkali and cellulose. Ions of modifying metals can also be retained on the surface of a molecular network of dissolved fibers by elements of supramolecular structures.

The treatment of expanded graphite with metal-substituted cellulose solution leads to a uniform distribution of cellulose fibers and metal ions held by it due to the additional electrostatic interaction of polar molecules with the electron-rich surface of graphite particles.

The method is confirmed by specific examples.

Example 1. 1 g of cellulose (aspen) is mixed in 29.4 ml of 8.5% aqueous NaOH solution, the resulting suspension is frozen at liquid nitrogen temperature for 2 minutes, the mass is thawed at room temperature, after which 20.6 ml of distilled water is added to a viscous gel-like solution and mixed get 50 ml of a homogeneous solution containing 2% cellulose in 5% NaOH solution. The prepared cellulose solution is mixed with expanded graphite grade OG-4 in a ratio of 1: 1 for one hour at room temperature. Then the resulting mass is stirred under reduced pressure to remove voids in the pores of graphite. After filtering and drying at 110 ° C, the composition in an inert gas atmosphere is subjected to heat treatment at a heating rate of 4 ° C / min to a temperature of 600 ° C, with exposure at a final temperature for 1 hour.

The resulting composite material has a microporous structure (pore diameter 16.5 nm), specific surface _area S _BET 55.4 m ² / g and the following sorption characteristics: iodine activity - 38.38 mg / g, methylene blue - 63.80 mg / g (see tables 1 and 2).

Example 2. Pre-prepare a 1% solution of cellulose in an aqueous solution of sodium hydroxide, for which 0.3 g of cellulose (aspen) is mixed in 29.4 ml of 8.5% NaOH. Further preparation of the composition is carried out analogously to example 1, but without additional dilution with water. The resulting composite material is largely microporous, but has a lower specific surface area (about 42 m ² / g). It is likely that with a higher content of activating agent during carbonization, a partial retention of the released carbon dioxide (CO ₂ ) occurs by the products of transformation of the alkaline component (oxides, carbonates), which inhibits the development of porosity in the final product.

Example 3. The method for producing the composite material is carried out analogously to example 1, but the composite mixture is subjected to molding in the form of granules with a size of 5 × 5 × 8 mm using a triple degree of compaction before drying in a wet, slightly viscous state. The formed composite material has better sorption qualities with respect to the absorption of iodine (69.44 mg / g) than powder, which occurs due to an increase in the number of sorbing pores per unit volume.

Example 4. The composition is prepared under the conditions of example 3, but take the ratio of cellulose (industrial cellulose, Bratsk) and expanded graphite 2.5: 1. The loosening and partial destruction of the granules observed during the heat treatment is the result of a decrease in the cohesiveness of the cellulose solution due to the increased level of activating alkaline agent. A noticeable sorption activity with respect to iodine (224.12 mg / g) is probably due to an increase in the total porosity of the material caused by the wedging of weakly bonded adhesive forces of flattened pores.

Example 5. The preparation of the composition is carried out under the conditions of example 1, but copper acetate is introduced as a modifying additive to the cellulose solution in an amount of 2% based on the introduced metal. Further interaction of solutions of Cu-containing cellulose with thermally expanded graphite GSM-1 (NGA) is carried out in accordance with example 1. The resulting porous (S _BET = 120 m ² / g) copper-containing carbon material has catalytic properties and exhibits sorption activity with respect to iodine and methylene blue (Table 2). In the described manner, composite systems were prepared containing from 2 to 5% copper in the composition of the applied cellulose solutions.

Studies of the structure of composite samples showed that the matrix of the carbon carrier, which determines the texture characteristics in the finished composite, is represented by two-dimensional well crystallized layers of graphite and a graphitized layered structure formed from a cellulose precursor. The dispersed phase of copper crystallites in a composite material prepared using a 2-3% modifying copper additive is mainly represented by metal particles 2-5 nm in size. In the case of using 5% of the copper content in the initial composition, the final carbon material contained copper particles up to 20 nm in size. The increase in size occurs due to the fusion of particles during carbonization.

Example 6. The preparation of the composite material is carried out under the conditions of example 4, characterized in that as an alkaline agent using a 20% solution of tetraethylammonium hydroxide (TU 6-00-05-132-78). The resulting product has a more developed specific surface area (S _BET = 108.55 m ² / g) than that obtained using sodium hydroxide as an alkaline agent, due to the promoting effect of volatile decomposition products released during carbonization.

The high cost of tetraethylammonium hydroxide and its significant reactivity with respect to cellulose limits the practical use of this reagent for the preparation of compositions based on cellulose solutions.

Example 7. The preparation of the composite mixture and its heat treatment is carried out in accordance with example 3, but the final carbonization temperature is increased to 800 ° C. The observed slight decrease in the strength of the granules is caused by the intense process of burning active carbon in the expanded graphite matrix, leading to texture changes in the resulting adsorbent. The carbonization process at 600 ° C leads to similar results when the exposure time of the composition was increased to 3 hours, or when high rates of temperature rise (10 ° C / min) were used. It was found that high heating rates (> 10 ° C / min) and / or prolonged curing of the composition at T≥800 ° C lead to disordering, weakening, and even destruction of the structure of the blocks.

Example 8. The preparation of the composition is carried out under the conditions of example 5, but nickel nitrate nitrate Ni (NO ₃ ) ₂ is introduced as a modifying additive to the cellulose solution in an amount of 2% per metal to be introduced. Further interaction of the solution of Ni-containing cellulose with thermally expanded graphite was carried out in accordance with Example 1. As a result of the heat treatment, a powdery carbon composite material was obtained (S _BET = 57.5 m ² / g), which could find its application in catalysis. The activity of the Ni-containing composite material with respect to methylene blue and iodine is not worse than the adsorption capacity of the individual components due to the fact that the availability of pores for the adsorption of liquids does not decrease during the preparation of the composition.

Example 9. The preparation of the composition is carried out under the conditions of example 5, but the hydrochloric complex of palladium H ₂ PdCl _{4 is} introduced as a modifying additive to the alkaline cellulose solution in an amount of 2% per metal to be introduced. Prepared Pd-containing cellulose solution is mixed with expanded graphite brand NGA in a mass ratio of 2: 1. The obtained microporous samples have significantly lower specific surface values (S _BET ~ 20 m ² / g) and high micropore surface values (S _micro = 300 m ² / g). The presence of a large number of ultramicropores in composite Pd-containing samples, inaccessible for adsorption of large molecules, explains the low values of sorption activity with respect to iodine and methylene blue. Palladium-containing carbon material is active in the hydrogenation of hexene-1 and cyclohexene.

Example 10. The preparation of the composite material is carried out under the conditions of the prototype, i.e. powdered cotton pulp is mixed with an activating agent and expanded graphite OG-4. The introduction of a modifying solution of Cu (CH ₃ COO) ₂ in the resulting suspension leads to an inhomogeneous distribution of the metal among the components of the composition. The implementation of the carbonization process with aging at a final temperature (600 ° C) for 5 hours leads to a significant loss of active carbon in the composition. The texture and sorption characteristics of the final product are close to the parameters of expanded graphite, i.e., preparation of the composition under the conditions of the prototype gives worse results compared to the proposed method.

An analysis of the presented results indicates that the optimal conditions for the preparation of composite material are: the use of a 1-2% solution of cellulose, a temperature rise rate of 4 ° C / min, a final temperature of 600 ° C and a holding time of 1 hour. Based on experimental data, it was found that for cases of diluted cellulose solutions with a concentration of less than 1%, the adhesion of the composite material decreases, the block composite becomes less dense and less solid.

Thus, the use of the proposed method of preparing a composition based on a solution of cellulose and expanded graphite makes it possible to simplify the preparation of a composite material and to obtain it in a much shorter time compared to the prototype. The use of cellulosic material in the form of a solution provides a homogeneous mixture of expanded graphite, dissolved cellulose fibers and a modifying additive without the use of a binder. The introduction of modifying metals into the composition in the form of metal-substituted celluloses gives the composite materials catalytic and adsorption properties, which makes it possible to use them as porous carbon adsorbents, carriers, and metal-containing catalysts, for example, for oligomerization and hydrogenation of olefins.

Table 1
Characterization of the starting components of graphite and cellulose Sample Treatment C ^* N ^* N ^* Graphite ^** intercalated (Noginsk); OG-4 NHO ₃ (conc.) 94.51-94.90 0.17-0.19 0.78-1.01 Expanded graphite OG-4 900 ° C, 1 min 96.96-97.20 0.06-0.09 0,03 GSM-1 graphite intercalated (Zavalevsk); NGV NHO ₃ + CH ₃ COOH 94.98-95.20 0.36-0.42 0.58 NGV expanded graphite 900 ° C, 1 min 97.94-98.58 0.09-0.15 0 GSM-1 graphite intercalated; Nga NHO ₃ (conc.) 94.85-95.57 0.18-0.15 0.97-1.10 Expanded Graphite NGA 900 ° C, 1 min 96.54-98.02 0.12-0.18 0,03 Industrial cellulose (Bratsk), ChP Fibers 7 × 1.0 × 1.5 mm 44.49 6.21 0 Microcrystalline Cellulose (Aspen) Particles 0.5 × 1.0 × 1.5 mm 45.69 6.31 0 Cotton Cellulose (Avicel) powder 45.56 6.28 0 Note: ^* content of elements, wt.%;
^** Natural anesthetized graphites were used, the content of impurities did not exceed 0.05 wt.%.

table 2
Sorption characteristics of carbon materials Experience number Sample Specific surface area; S _BET , m ² / g Iodine activity; mg / g Activity on methylene blue; mg / g OG-4 36.5 less than 10 less than 10 Nga 12.7 11.83 17.27 NGV 33 25.45 21.17 one 2% solution of cellulose, aspen (5% NaOH) + OG-4 (1: 1). Powder 55,4 38.38 63.80 2 1% solution of cellulose, aspen (8.5% NaOH) + OG-4 (1: 1). Powder 42.0 35.86 45.17 3 2% solution of cellulose, aspen (5% NaOH) + OG-4 (1: 1). Granules 60.75 69.44 41.02 four 2% cellulose solution (Bratsk) + NGV (2.5: 1). Granules 94.06 224.12 13.30 5 Cu / 2% p-p cellulose (aspen), 5% p-p NaOH + HGA (2: 1: 1). Powder 120.10 71.80 38.62 6 2% pp cellulose cotton, (C ₂ H ₅ ) ₄ NOH, + HBV (2.5: 1). Granules 108.55 148.29 37.72 7 Sample 3, 800 ° C 51.70 28.38 65.48 8 Ni / 2% p-p cellulose (aspen), 5% p-p NaOH + HGA (2: 1: 1). Powder 57.5 48,20 36.87 9 Pd / 2% p-p cellulose (aspen), 5% p-p NaOH + HGA (2: 1: 1). Powder 20.40 22.13 24.80 10 Proto Type Cellulose (cotton) + OG-4 (1: 1) 45.90 27.12 33.41

Claims (2)

1. A method of obtaining a composite material, comprising preparing a composition consisting of expanded graphite, cellulose and an aqueous solution of an activating agent, and its carbonization with a heating rate of 4 ° C / min to 600 ° C, characterized in that 1-2% are first prepared - cellulose solution in an activating agent, which is used as a 5-8.5% sodium hydroxide solution, to prepare the composition, the resulting solution is mixed with expanded graphite in a mass ratio of (1-2.5) :( 2-1), respectively, and carbonization is carried out, keeping the irradiated composition at the above temperature for 1 hour 2. The method according to claim 1, characterized in that 2-5 wt.% Of a transition metal modifying compound in terms of metal are added to the cellulose solution to impart catalytic and adsorption properties to the composite material.